Axis Of Goldfish Research Articles

Nesfatin-1 is an inhibitor of the growth hormone-insulin-like growth factor axis in goldfish (Carassius auratus).

Nesfatin-1, an 82 amino acid peptide cleaved from the N-terminal of its precursor nucleobindin-2 (NUCB2), is emerging as a multifunctional peptide in fish. The present study aimed to determine whether nesfatin-1 plays a role in fish somatic growth by modulating the growth hormone (GH)/insulin-like growth factor (IGF) axis, using a representative teleost model, the goldfish (Carassius auratus). The results demonstrated that a single i.p. injection of synthetic goldfish nesfatin-1 significantly decreased the expression of hypothalamic pacap (approximately 90%) and pituitary Gh (approximately 90%) mRNAs at 15minutes post-injection. Serum GH levels were also reduced as a result of nesfatin-1 administration, by approximately 45% and 55% at 15 and 30minutes post-injection, respectively. Likewise, in vitro treatment of goldfish dispersed pituitary cells with nesfatin-1 reduced Gh secretion, suggesting that nesfatin-1 acts directly on pituitary somatotrophs to inhibit Gh release. Exposure of cultured liver fragments to nesfatin-1 (0.1, 1 and 10nmolL-1 ) led to a significant reduction in igf-1 mRNA at 120minutes and of igf-II mRNA at 30 and 60minutes post-incubation. Collectively, these results indicate a suppressive role for nesfatin-1 on the goldfish GH/IGF axis. Immunohistochemical studies demonstrated that NUCB2/nesfatin-1-like immunoreactivity, although present in the goldfish pituitary, is not colocalised with GH in goldfish somatotrophs. Thus, nesfatin-1 does not appear to act in an autocrine manner to regulate GH secretion. Taken together, this research found that the pituitary gland is an important source of endogenous NUCB2/nesfatin-1 and also that nesfatin-1 directly suppresses the Gh/IGF axis in goldfish.

The Lack of Light-Dark and Feeding-Fasting Cycles Alters Temporal Events in the Goldfish (Carassius auratus) Stress Axis.

Simple SummaryThe circadian system synchronizes physiology and behavior to predictable environmental variations (daily cycles in light, temperature, or food availability). To this purpose, animals possess endogenous oscillators that provide internal temporal signals, thanks to rhythmic clock gene expression. In mammals, disruption of circadian oscillators correlates to overactivation of the stress axis, but this connection is less well known in teleosts. This work aims to learn how the absence of two main external signals (light-dark cycle and feeding schedule) impacts the oscillators in the hypothalamus-pituitary-interrenal) axis of goldfish, studying rhythms in locomotor activity, circulating cortisol, and clock gene expression. The removal of environmental synchronizators caused an increase in basal cortisol levels, indicating stress. Constant darkness also overrode clock gene rhythms in the whole axis but did not impede food anticipatory activity. Feeding at random times disrupted the interrenal clock, but cortisol and activity rhythms remained, concluding that clock gene rhythms in the interrenal tissue are unnecessary for rhythmic cortisol release or diurnality. This work evidences how environmental conditions impact the HPI axis, affecting endocrine and circadian functioning, which need to be considered when progressing towards optimizing fish welfare.Vertebrates possess circadian clocks, driven by transcriptional–translational loops of clock genes, to orchestrate anticipatory physiological adaptations to cyclic environmental changes. This work aims to investigate how the absence of a light-dark cycle and a feeding schedule impacts the oscillators in the hypothalamus-pituitary-interrenal axis of goldfish. Fish were maintained under 12L:12D feeding at ZT 2; 12L:12D feeding at random times; and constant darkness feeding at ZT 2. After 30 days, fish were sampled to measure daily variations in plasma cortisol and clock gene expression in the hypothalamus-pituitary-interrenal (HPI) axis. Clock gene rhythms in the HPI were synchronic in the presence of a light-dark cycle but were lost in its absence, while in randomly fed fish, only the interrenal clock was disrupted. The highest cortisol levels were found in the randomly fed group, suggesting that uncertainty of food availability could be as stressful as the absence of a light-dark cycle. Cortisol daily rhythms seem to depend on central clocks, as a disruption in the adrenal clock did not impede rhythmic cortisol release, although it could sensitize the tissue to stress.

Response of the thyroid axis and appetite-regulating peptides to fasting and overfeeding in goldfish (Carassius auratus)

The thyroid axis is a major regulator of metabolism and energy homeostasis in vertebrates. There is conclusive evidence in mammals for the involvement of the thyroid axis in the regulation of food intake, but in fish, this link is unclear. In order to assess the effects of nutritional status on the thyroid axis in goldfish, Carassius auratus, we examined brain and peripheral transcripts of genes associated with the thyroid axis [thyrotropin-releasing hormone (TRH), thyrotropin-releasing hormone receptors (TRH-R type 1 and 2), thyroid stimulating hormone beta (TSHβ), deiodinase enzymes (DIO2, DIO3) and UDP-glucoronsyltransferase (UGT)] and appetite regulators [neuropeptide Y (NPY), proopiomelanocortin (POMC), agouti-related peptide (AgRP) and cholecystokinin (CCK)] in fasted and overfed fish for 7 and 14 day periods. We show that the thyroid axis responds to overfeeding, with an increase of brain TRH and TSHβ mRNA expression after 14 days, suggesting that overfeeding might activate the thyroid axis. In fasted fish, hepatic DIO3 and UGT transcripts were downregulated from 7 to 14 days, suggesting a time-dependent inhibition of thyroid hormone degradation pathways. Nutritional status had no effect on circulating levels of thyroid hormone. Central appetite-regulating peptides exhibited temporal changes in mRNA expression, with decreased expression of the appetite-inhibiting peptide POMC from 7 to 14 days for both fasted and overfed fish, with no change in central NPY or AgRP, or intestinal CCK transcript expression. Compared to control fish, fasting increased AgRP mRNA expression at both 7 and 14 days, and POMC expression was higher than controls only at 7 days. Our results indicate that nutritional status time-dependently affects the thyroid axis and appetite regulators, although no clear correlation between thyroid physiology and appetite regulators could be established. Our study helps to fill a knowledge gap in current fish endocrinological research on the effects of energy balance on thyroid metabolism and function.

Endocrine disrupting effects of waterborne fluoxetine exposure on the reproductive axis of female goldfish, Carassius auratus

Evidence suggests that pharmaceuticals and personal care products reach urban watersheds, bioconcentrate in fish, and potentially disrupt physiological homeostasis. These impairments often affect hormone functions. Selective serotonin reuptake inhibitors (SRRIs) are increasingly studied with regards to their endocrine disrupting effects on teleost physiological processes, including reproduction. To examine whether FLX effects on the endocrine regulation of reproductive physiology in goldfish are sex-specific, we exposed sexually recrudescent female goldfish to two waterborne concentrations of FLX (0.54μg/L and 54μg/L) using an experimental design previously used for sexually mature male goldfish. To evaluate possible endocrine disrupting effects, we quantified the gonadosomatic index, circulating hormone concentrations (luteinizing hormone, LH; growth hormone, GH; 17-β estradiol, E2; and testosterone, T), and the expression of isotocin and vasotocin in the telencephalon, gonadotropin subunits and GH in the pituitary, and gonadotropin receptors, GH receptors, and aromatase in the ovary. Female goldfish exposed to 0.54μg/L FLX exhibited a significant decrease in circulating E2, and conversely, a significant increase in circulating LH and ovarian aromatase mRNA levels, suggesting disruption of E2-mediated feedback on LH release. These results, when compared with those previously observed in males, reveal that waterborne exposure to environmentally relevant levels of FLX sex-specifically disrupts the reproductive endocrine axis in goldfish, characterized by a decrease in E2 in females, and conversely, estrogen-like effects in males. These data emphasize the importance of studying the effect of endocrine disrupting chemicals on both sexes.

Molecular identification of the Dyn/Kor system and its potential role in the reproductive axis of goldfish

To ascertain the significance of the dynorphin/kappa-opioid receptor (Dyn/Kor) system in fish reproduction, prodynorphin (pdyn) cDNA was cloned from goldfish. Two Dyn peptides (DynA and DynB) are present in the goldfish prodynorphin precursor. Both DynA and DynB are biologically active as they are able to functionally interact with the goldfish Kor expressed in cultured eukaryotic cells to suppress forskolin-induced CRE promoter activity. RT-PCR analysis showed that pdyn is widely expressed in brain regions, with the highest expression in hypothalamus. During ovarian development, hypothalamic pdyn and kor mRNA levels are lower in the early vitellogenic stage. Then the biological effects of Dyn peptides on salmon gonadotropin releasing hormone (sgnrh), luteinizing hormone beta (lhb) and follicle stimulating hormone beta (fshb) mRNA synthesis were further investigated in goldfish. Intraperitoneal injections of DynA and DynB significantly reduced hypothalamic sgnrh and pituitary lhb and fshb mRNA levels in male goldfish, but these two peptides only down-regulated sgnrh and lhb mRNA expression in female goldfish. In vitro studies revealed that DynA also decreased lhb mRNA levels in primary cultures of pituitary cells, indicating that this peptide can exert its actions at the pituitary level. Our findings suggest that the Dyn/Kor system plays a negative role in regulating the reproductive axis in goldfish.

Nesfatin-1 Regulates the Hypothalamo-Pituitary-Ovarian Axis of Fish1

Nesfatin-1 is an anorexigen in goldfish. In the present study, we provide novel data indicating the presence and regulatory effects of nesfatin-1 on the hypothalamo-pituitary-ovarian (HPO) axis of goldfish. Nucleobindin-2 (NUCB2)/nesfatin-1-like immunoreactive (ir) cells are present in the hypothalamus and in the pituitary, suggesting a hypophysiotropic role for nesfatin-1. NUCB2/nesfatin-1-like ir cells colocalize gonadotropin-releasing hormone (GnRH) in the nucleus lateralis tuberis posterioris and the nucleus anterior tuberis of the goldfish hypothalamus. The presence of nesfatin-1 with GnRH in these two nuclei implicated in pituitary hormone release suggests a role for nesfatin-1 on gonadotropin secretion. A single i.p. injection of synthetic goldfish nesfatin-1 (50 ng/g body wt) resulted in an acute decrease (∼75%) in the expression of hypothalamic chicken GnRH-II and salmon GnRH mRNAs at 15 min postinjection in goldfish. Meanwhile, pituitary luteinizing hormone (LH) beta and follicle-stimulating hormone beta mRNAs were also inhibited (∼80%), but only at 60 min postinjection. Nesfatin-1 administration also resulted in a significant reduction (∼60%) in serum LH levels at 60 min postadministration. Nesfatin-1-like immunoreactivity was also found in the follicle cells, but not the oocytes, in zebrafish and goldfish ovaries. Incubation of zebrafish follicles with nesfatin-1 resulted in a significant reduction in basal germinal vesicle breakdown (∼50%) during the oocyte maturation. In addition, nesfatin-1 also attenuated the stimulatory effects of maturation-inducing hormone on germinal vesicle breakdown. Together, the current results indicate that nesfatin-1 is a metabolic hormone with an inhibitory tone on fish reproduction. Nesfatin-1 appears to elicit this suppressive effect through actions on all three tissues in the fish HPO axis.