Neuropeptides in the Australian lungfish Neoceratodus forsteri: effects in vivo and presence in autonomic nerves

Central ventilatory and cardiovascular actions of trout gastrin-releasing peptide (GRP) in the unanesthetized trout

Gastrin-releasing peptide (GRP), a neuropeptide initially isolated from porcine stomach, shares sequence similarity with bombesin. GRP and its receptors are present in the brains and peripheral tissues of several species of teleost fish, but little is known about the ventilatory and cardiovascular effects of this peptide in these vertebrates. The goal of this study was to compare the central and peripheral actions of picomolar doses of trout GRP on ventilatory and cardiovascular variables in the unanesthetized rainbow trout. Compared to vehicle, intracerebroventricular (ICV) injection of GRP (1–50 pmol) significantly elevated the ventilation rate (ƒV) and the ventilation amplitude (VAMP), and consequently the total ventilation (VTOT). The maximum hyperventilatory effect of GRP (VTOT: +225%), observed at a dose of 50 pmol, was mostly due to its stimulatory action on VAMP (+170%) rather than ƒV (+20%). In addition, ICV GRP (50 pmol) produced a significant increase in mean dorsal aortic blood pressure (P_DA) (+35%) and in heart rate (ƒH) (+25%). Intra-arterial injections of GRP (5–100 pmol) were without sustained effect on the ventilatory variables but produced sporadic and transient increases in ventilatory movement at doses of 50 and 100 pmol. At these doses, GRP elevated P_DA by +20% but only the 50 pmol dose significantly increased HR (+15%). In conclusion, our study suggests that endogenous GRP within the brain of the trout may act as a potent neurotransmitter and/or neuromodulator in the regulation of cardio-ventilatory functions. In the periphery, endogenous GRP may act as locally-acting and/or circulating neurohormone with an involvement in vasoregulatory mechanisms.

Evidence that neurotensin mediates postprandial intestinal hyperemia in the python, Python regius

Digestion of large meals in pythons produces substantial increases in heart rate and cardiac output, as well as a dilation of the mesenteric vascular bed leading to intestinal hyperemia, but the mediators of these effects are unknown. Bolus intra-arterial injections of python neurotensin ([His3, Val4, Ala7]NT) (1 − 1,000 pmol/kg) into the anesthetized ball python Python regius ( n = 7) produced a dose-dependent vasodilation that was associated with a decrease in systemic pressure (Psys) and increase in systemic blood flow (Qsys). There was no effect on pulmonary pressure and conductance. A significant ( P < 0.05) increase in heart rate ( fH) and total cardiac output (Qtot) was seen only at high doses (>30 pmol/kg). The systemic vasodilation and increase in Qtot persisted after β-adrenergic blockade with propranolol, but the rise in fH was abolished. Also, the systemic vasodilation persisted after histamine H2-receptor blockade. In unanesthetized pythons ( n = 4), bolus injection of python NT in a dose as low as 1 pmol/kg produced a significant increase in blood flow to the mesenteric artery (177% ± 54%; mean ± SE) and mesenteric conductance (219% ± 74%) without any increase in Qsys, systemic conductance, Psys, and fH. The data provide evidence that NT is an important hormonal mediator of postprandial intestinal hyperemia in the python, but its involvement in mediating the cardiac responses to digestion may be relatively minor.

Selected pathological, immunohistochemical and ultrastructural changes associated with an infection by Diphyllobothrium dendriticum (Nitzsch, 1824) (Cestoda) plerocercoids in Coregonus lavaretus (L.) (Coregonidae)

The pathological changes induced by an infection of Diphyllobothrium dendriticum (Nitzsch, 1824) plerocercoids in powan, Coregonus lavaretus (L.), from Loch Lomond, Scotland, were assessed using immunohistochemical and ultrastructural techniques. In a sample of 26 powan, the occurrence of encysted plerocercoids of D. dendriticum on the outer surface of the stomach was 38.5% (n = 10) with the number of cysts ranging from 4 to 15 and measuring 4.2 +/- 1.0 mm x 3.4 +/- 0.9 mm (mean +/- SD). Histological examination of intestinal samples also revealed plerocercoids (2-21) encapsulated within a proliferation of mesenteric fibrous tissues of the gastric wall and, occasionally, by the gut lamina propria-submucosa and lamina muscularis. In section, cysts were tri-layered and were formed from a series of concentric whorls of fibroblast and collagen fibre-based connective elements. The extent of necrosis within each muscle layer and the serosa of the stomach differed, notably within the latter that was marked by a chronic inflammatory reaction and fibrosis. Within the cyst and around it, a large number of degranulating mast cell/eosinophilic granule cells were seen, in addition to melano-macrophage centres. Immunohistochemical staining of sections of infected stomach revealed a high density of elements, in close proximity to plerocercoids, staining positive for serotonin, bombesin, substance P and galanin. Uninfected material did not present the same levels of activity. Sections through both infected and uninfected tissue were also tested for elements containing vasoactive intestinal peptide, met-enkephalin, calcitonin gene-related peptide, neuropeptide Y and nitric oxide synthase, but these were absent.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

The presence of a galanin-like peptide in the gut neuroendocrine system of Lampetra fluviatilis and Acipenser transmontanus: an immunohistochemical study

Galanin is a brain-gut neuropeptide present in the central and peripheral nervous systems of vertebrates. In the present survey, the galaninergic and the diffuse endocrine systems of the alimentary canal of the river lamprey, Lampetra fluviatilis, and the white sturgeon, Acipenser transmontanus, were studied by immunohistochemistry. The results show the presence of galanin-like immunoreactive endocrine cells in the gut of L. fluviatilis. In addition, a galanin-like immunoreactivity was detected in enteric intramural neurons of both species. It is conceivable that the galaninergic system plays in both species a role in the regulation of the gut muscle contractility and in the modulation of mucosal secretive/absorptive processes. In A. transmontanus, the presence of galanin-like immunoreactive nerve fibres associated with components of the gut associated-lymphoid tissue is possibly correlated with a control of the defensive events at this site. The presence of a galanin-like immunoreactivity in the neuroendocrine system of these two ancient fishes confirms the hypothesis on the early occurrence of this regulative molecule in the gastro-enteric system of vertebrates.

An immunocytochemical study of intrapancreatic ganglia, nerve fibres and neuroglandular junctions in Brockmann bodies of the tompot blenny (Blennius gattoruggine), a marine teleost

The innervation of the Brockmann bodies in the teleost fish, Blennius gattoruggine, was studied using immunocytochemical techniques at both the light and electron microscopy levels. Islet innervation consisted of intrapancreatic ganglia, generally localized inside the rim of the exocrine tissue of the Brockmann bodies, in proximity to the islet, nerve fibres and nerve terminals with synaptic complexes. The intrapancreatic ganglia were of variable size, with different numbers of ganglionic cells, that appeared unipolar in section. The cell bodies showed immunoreactivity to galanin, oxytocin, peptide tyrosine tyrosine and glucagon. The extrinsic and intrinsic nerve fibres passed through the exocrine parenchyma and crossed the connectival septa and islet connectival sheath, penetrating into the islets, where they became increasingly thinner. They terminated on the endocrine cells with dilated nerve terminals. At least three types of terminals were detected, depending on the different vesicle content: peptidergic, cholinergic or adrenergic. They presented specialized synaptic structures, the neuroglandular junctions, some of which contained neurosecretory granules immunogold labelled by galanin antiserum. This new finding confirms the role of galanin as a neurotransmitter. This rich supply of innervation may be important in the regulation and integration of islet secretion.

Vip-induced relaxation of small arteries of the rainbow trout, Oncorhynchus mykiss, involves prostaglandin synthesis but not nitric oxide

Small arteries (internal diameter 376 +/- 69 microns) from the proximal intestine region of the rainbow trout were mounted in a myograph apparatus where changes in isometric tension could be recorded. VIP (vasoactive intestinal polypeptide) caused a concentration-dependent relaxation (10(-9)-3 x 10(-7) M) of vessels precontracted with the alpha-adrenoceptor agonist phenylephrine (10(-5) M). The nitric oxide synthase inhibitor L-NAME (10(-4) M) did not affect the VIP-relaxation, neither did the lipoxygenase inhibitor esculetin (10(-5) M). However, the cyclooxygenase inhibitor indomethacin (10(-6) M) shifted the concentration-response curve significantly to the right. The VIP-relaxation was still present after mechanical removal of the endothelium. Sodium nitroprusside (10(-9)-10(-6) M) caused a concentration-dependent relaxation of the precontracted vessel, indicating the presence of soluble guanylate cyclase in the vascular smooth muscle cells. VIP-immunoreactivity was found in varicose nerve fibers in these vessels, but nitric oxide synthase-immunoreactivity could not be demonstrated. These results suggest that in rainbow trout, as in mammals, VIP is an endogenous vasodilating neuropeptide. No endothelium-dependent mechanism seems to be involved, neither is production of nitric oxide. Instead the relaxation is mediated, at least in part, via prostaglandin synthesis.