Seasonal variations of trimethylamine oxide and urea in the blood of a cold-adapted marine teleost,the rainbow smelt

Trimethylamine oxide (TMAO), which has previously not been known to occur in significant amounts in the blood of marine teleosts, rose to concentrations of approximately 50 mM in the blood of winter-acclimatized rainbow smelt, Osmerus mordax. Urea also increased in the blood of cold-acclimatized smelt, and, with TMAO, contributed significantly to the winter freezing point depression. TMAO and urea also varied seasonally in muscle and liver tissues. TMAO and urea appeared to be reabsorbed from the urine. Losses of TMAO and urea from the head region of the fish, where most of the losses appeared to occur, were approximately 9 μmol and 8 μmol 100 g⁻¹ h⁻¹, respectively. Despite the effluxes, TMAO and urea levels in both the blood and muscle either increased or were maintained in starved, cold-acclimated fish, suggesting that they were synthesized in response to cold temperature. TMAO was also found in the blood of some other cold-hardy teleosts.     

Dopamine inhibits gonadotropin secretion in the Chinese loach (Paramisgurnus dabryanus)

The effects of dopamine on gonadotropin (GtH) secretion in sexually mature Chinese loach were investigated. Spontaneous secretion of GtH was inhibited within 1 h following an intramuscular injection of dopamine (100 g/g body wt). Similarly, dopamine (50 and 100 g/g body wt) caused a significant reduction in serum GtH in fish with elevated GtH levels as a result of pretreatment with gonadotropin-releasing hormone (GnRH) analogs either alone or in combination with the dopamine receptor antagonist domperidone. In summary, the present study provides direct evidence that dopamine functions as a gonadotropin-release inhibitory factor in the Chinese loach by blocking spontaneous and GnRH-stimulated GtH release.     

The innervation pattern of fast myotomal muscle in the teleostMyoxocephalus scorpius: A reappraisal

The pattern of polyneuronal innervation in the sculpinMyoxocephalus scorpius was examined. The majority of fast fibres in sculpin are innervated by both adjacent nerves, and <15% receive input from sub-adjacent myotomes. Stimulation through both adjacent and sub-adjacent nerves results in muscle action potentials. Each adjacent nerve supplies 2–5 axons to a given fibre. A typical fibre is probably innervated by around 4–6 axons, and pre-terminal branching accounts for the 8–20 endplates present on these fibres.     

Thyroid hormones down-regulate thyrotropin β mRNA level in vivo in the turbot (Psetta maxima)

Thyroid stimulating hormone (TSH) is a vertebrate pituitary heterodimeric hormone that stimulates the thyroid gland to produce the thyroid hormones, T3 and T4. We report here the cloning, by PCR on reverse-transcribed pituitary RNAs, of a 180 bp fragment of the cDNA encoding TSH subunit in the turbot (Psetta maxima). The deduced amino acid sequence displayed 66 and 75% identity with the corresponding sequence from the European eel (Anguilla anguilla) and the rainbow trout (Oncorchyncus mykiss), respectively. This cDNA was then used as a probe for densitometric analysis of individual pituitary Northern blots. TSH mRNA levels were quantified in turbot where circulating thyroid hormones were modified by dietary treatments or hormone supplementation. Recombinant rainbow trout growth hormone had no effect on circulating thyroid hormone levels or on pituitary TSH mRNA level. In turbot fed heat-treated rapeseed meal, plasma T4 levels were lowered and TSH mRNA increased more than two fold. In contrast, when turbot were fed a standard fish-meal supplemented with T3, circulating T3 levels were elevated and there was a dramatic decrease in TSH mRNA level. It is concluded that both thyroid hormones are able to down-regulate TSH mRNA level in vivo in the turbot. These results are discussed in the context of the evolution of the TH feed-back on TSH production.     

The tilapia prolactin cell: A model for stimulus-secretion coupling

The tilapia prolactin (PRL) cell responds rapidly (10–20 min) to small physiological changes in medium osmotic pressure (OP), releasing increasing quantities of hormone as medium OP is reduced. This release is rapidly (≤ 10 min) inhibited by somatostatin (SRIF). There is now extensive evidence that tilapia PRL cell function is regulated through the second messengers Ca⁺⁺ and cAMP. Our studies have shown that PRL release is augmented by treatments that lead to increased levels of intracellular Ca⁺⁺ or cAMP. On the other hand, PRL release is blocked when tissues are incubated in Ca⁺⁺-depleted medium or upon the addition of Co⁺⁺, an inhibitor of Ca⁺⁺-mediated processes. The use of⁴⁵Ca⁺⁺ to characterize the movement of Ca⁺⁺ into PRL cells has provided evidence that an increase in the influx of extracellular Ca⁺⁺ may participate in PRL release upon exposure to hyposmotic medium. Our studies have also shown that SRIF suppresses the increase in⁴⁵Ca⁺⁺ accumulation that is brought about when OP is reduced. We have also examined the effects of OP and SRIF on cAMP levels. The reduction of medium OP did not alter cAMP metabolism during 20 min of incubation. By contrast, cAMP accumulation in the presence of IBMX was enhanced at 1 hr of incubation in reduced OP. Thus, an increase in cAMP turnover may play a role in maintaining PRL release under sustained stimulation. SRIF reduced the accumulation of cAMP during 10 min of incubation with IBMX and also reduced the forskolin-stimulated increase in cAMP. Thus, SRIF may suppress adenylate cyclase activity. Finally, our studies have revealed that the forskolin-stimulated increase in cAMP levels is not dependent upon medium Ca⁺⁺. The presence of Ca⁺⁺ in the medium is required, however, for PRL release even when the cAMP messenger system has been activated. Moreover, cAMP accumulation was augmented when intracellular Ca⁺⁺ was increased. This raises the possibility that reduced OP may stimulate an increase in cAMP turnover indirectly through its action(s) on cytosolic Ca⁺⁺.     

Autonomic innervation of the ovary of the Atlantic cod,Gadus morhua

The autonomic innervation of the ovary of the Atlantic cod was investigated using histochemical and physiological/pharmacological methods. The paired ovary receives autonomic innervation via branches of the posterior splanchnic nerve (vesicular nerve).Histochemical studies demonstrated vasoactive intestinal polypeptide (VIP)-immunoreactive, 5-hydroxytryptamine-immunoreactive and adrenergic nerve fibers, but a number of antisera raised against other peptides failed to reveal any specific reaction in the tissue preparations. It is concluded that the cod ovary receives a double antagonistic autonomic innervation of excitatory cholinergic fibers and non-adrenergic inhibitory fibers. The nature of the inhibitory neurotransmitter is not known.     

Regulation of cardiac output and gut blood flow in the sea raven,Hemitripterus americanus

Coeliac artery blood flow (F_ca) before and after feeding was recorded in the sea raven. To obtain basic information about the scope of cardiovascular adjustment in the sea raven, a separate series of experiments was performed, in which ventral (P_va), and dorsal (P_da) aortic blood pressure, heart rate (HR) and cardiac output (jaz) were monitored during rest and encouraged exercise.Measurements of coeliac artery flow showed that visceral blood flow is substantial, particularly after feeding, and variations in the visceral vascular conductance affect P_da directly. Simultaneous recordings of intestinal and dorsal aortic blood pressures showed no measurable difference in the two arterial pressures, refuting the idea of a vascular control at the level of the main coeliac artery. Thus, in the sea raven, the adrenergic tonus affecting the visceral vasculature presumably acts at the arteriolar level.Sea ravens encouraged to exercise increased theirjaz by 64%; 32% through HR and 25% through stroke volume. The increase injaz during encouraged exercise was sufficient to produce an elevation of both P_va and P_da, despite an increase of systemic vascular conductance, -adrenoceptor blockade with sotalol, however, severely impaired the increase injaz during exercise, and the change in P_da was reversed.During rest there were both an adrenergic and a cholinergic tonus affecting the HR, as revealed by the effects of injected pharmacological antagonists. Swimming activity decreased the cholinergic tonus, while the adrenergic tonus increased.     

TGF-β系统及其在硬骨鱼中的研究进展

TGF-β（transforming growth factor-β）是一类多效应细胞因子,在很多生理活动中发挥功能。TGF-β以前体形式合成,随后被切割活化形成成熟的TGF-β。TGF-β以二聚体的形式发挥作用,与受体TβRI（transforming growth factor-β receptor I）和TβRII（transforming growth factor-β receptor Ⅱ）形成一个大型复合物后,磷酸化胞内的Smad,激活下游信号通路。鱼类中,对TGF-β家族成员的研究主要集中在对TGF-β1的研究,包括TGF-β1与免疫相关和与生殖相关的功能,也有研究表明TGF-β1与肝功能相关。此外,有少量对TGF-β家族其他成员和TGF-β受体的研究。     

The role of Toll‐like Receptors in innate immunity and infectious diseases of teleost

The immune defence mechanism depends mainly on germ‐line encoded pattern‐recognition receptors (PRRs). These PRRs respond to many exogenous pathogens and/or endogenous serious signals, by recognizing some highly conserved structures such as pathogen‐associated molecular patterns (PAMPs) and danger/damage associated molecular patterns (DAMPs). Till date, the most studied PRRs are Toll‐like receptors (TLRs). Upon activation of TLRs, there is production of inflammatory cytokines and type I interferons (IFNs) via myeloid differentiation primary response gene 88 (MyD88)‐dependent or ‐independent signalling, respectively, modulating innate and adaptive immunity, as well as inflammatory responses. In fish species studied to date, there are more than 17 TLRs that are identified with some showing homology to mammals, and some are unique for teleost. In the present review, more light are to be shed on the classification, structure and specific ligands of TLRs, with focuses on their signal pathways and different biological activities. Studies of TLRs and their role in the innate immune will potentially have implications for the prevention and treatment of fish diseases.