The effect of somatostatins (SRIF-14, 25 and 28), galanin and anti-SRIF on plasma growth hormone levels in Coho salmon (Oncorhynchus kisutch, Walbaum)

Porcine galanin, somatostatins (SRIF-25 and SRIF-28) and invariant SRIF-14, known to have inhibitory-stimulatory actions on growth hormone (GH) secretion in higher vertebrates, were tested for their ability to affect plasma GH levels in coho salmon. Peptides were administered by intraperitoneal injection of 10 or 100 ng g⁻¹ body weight. All three SRIFs decreased plasma GH concentrations, their activity following the order SRIF-14 > SRIF-28 > SRIF-25. Galanin and an anti-SRIF produced pronounced, although transient increases in plasma GH.     

The caudal spinal cord of coho salmon (Oncorhynchus kisutch): Immunocytochemical evidence of a “caudal serotoninergic system”

Summary The caudal spinal cord of the coho salmon was investigated by means of immunocytochemistry using antisera against serotonin, urotensin I, urotensin II, somatostatin and a urea-extract of bovine Reissner's fiber (AFRU). Populations of serotonin-immunoreactive (IR) neurons were found rostral and dorsal to the urophysis in close spatial association with caudal secretory neurons. Thick, smooth serotonin-IR processes extended toward the external surface of the spinal cord where they displayed conspicuous terminal dilatations. Thin, beaded serotonin-IR fibers appeared to innervate populations of caudal secretory and somatostatin-IR cerebrospinal fluid-contacting neurons. Most caudal neurosecretory cells displayed both urotensin I and urotensin II immunoreactivities; only a minority reacted exclusively with either urotensin I or urotensin II antisera. Urotensin II-IR and somatostatin-IR cerebrospinal fluid (CSF)-contacting neurons were found as an integral component of the central canal wall in the caudal spinal cord and filum terminale; their dendritic processes appeared to contact Reissner's fiber, which displayed a weak AFRU-immunoreactivity while inside the central canal, but became strongly reactive in the interior of the terminal ventricle as it formed the massa caudalis. The distribution of serotoninergic processes points to a regulatory role in the function of caudal secretory and CSF-contacting neurons and to a putative serotonin release into the subarachnoid space and/or meningeal vasculature. It is also suggested that the CSF-contacting neurons of the central canal may participate in a feedback mechanism controlling the secretory activity of the subcommissural organ.Supported by Grant A/1095-1 from the International Foundation for Science, Sweden, to C.Y.; Grant I/63-476 from Volkswagen-Stiftung to E.R.; and Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile     

Some peptide-like colocalizations in endocrine cells of the pyloric caeca and the intestine of Oncorhynchus mykiss (Teleostei)

Summary The coexistence of immunoreactivities to cholecystokinin, glucagon, glucagon-like peptide 1, salmon pancreatic polypeptide, neuropeptide tyrosine, and peptide tyrosine tyrosine was studied immunocytochemicaly, revealing for the first time in fish intestine the existence in the same cell of immunoreactivities to cholecystokinin-glucagon/glucagon-like peptide 1, cholecystokinin-salmon pancreatic polypeptide, glucagon/glucagon-like peptide 1-salmon pancreatic polypeptide, glucagon/glucagon-like peptide 1-neuropeptide tyrosine, salmon pancreatic polypeptide tyrosine tyrosine, and glucagon/glucagon-like peptide 1-peptide tyrosine tyrosine. Colocalization of cholecystokinin-salmon pancreatic polypeptide was observed only in the pyloric caeca of the rainbow trout Oncorhynchus mykiss, while the other colocalizations also occurred in proximal and middle intestinal segments. In all cases, endocrine cells immunoreactive to only one of the paired antisera were detected except for anti-glucagon and anti-glucagon-like peptide 1, which always immunostained the same cells.     

The role of visual cues in the facilitation of growth in a schooling fish

Synopsis This study tested the hypothesis that visual contact between fish may result in enhanced rates of growth in a schooling fish. Juvenile chum salmon, Oncorhynchus keta, were held singly and reared in isolation or in visual contact with conspecifics. Fish were fed at either a low (6% body weight d^–1) or high (20% body weight d^–1) ration for 42d. Specific rates of weight gain were 18% greater at low ration and 38% greater at high ration for fish in visual contract with conspecifics than for those held in isolation. The results demonstrate a selective advantage of visual cues associated with schooling behavior and suggest that the efficacy of growth models for schooling fishes may be enhanced by the consideration of social interactions which may facilitate growth.     

The effects of endogenous or exogenous catecholamines on blood respiratory status during acute hypoxia in rainbow trout (Oncorhynchus mykiss)

Summary An extracorporeal circulation of rainbow trout (Oncorhynchus mykiss) was utilized to continuously monitor the rapid and progressive effects of endogenous or exogenous catecholamines on blood respiratory/acid-base status, and to provide in vivo evidence for adrenergic retention of carbon dioxide (CO₂) in fish blood (cf. Wood and Perry 1985). Exposure of fish to severe aquatic hypoxia (final P _wO₂=40–60 torr; reached within 10–20 min) elicited an initial respiratory alkalosis resulting from hypoxia-induced hyperventilation. However, at a critical arterial oxygen tension (P _aO₂) between 15 and 25 torr, fish became agitated for approximately 5 s and a marked (0.2–0.4 pH unit) but transient arterial blood acidosis ensued. This response is characteristic of abrupt catecholamine mobilization into the circulation and subsequent adrenergic activation of red blood cell (RBC) Na⁺/H⁺ exchange (Fievet et al. 1987). Within approximately 1–2 min after the activation of RBC Na⁺/H⁺ exchange by endogenous catecholamines, there was a significant rise in arterial PCO₂ (P _aCO₂) whereas arterial PO₂ was unaltered; the elevation of P _aCO₂ could not be explained by changes in gill ventilation. Pre-treatment of fish with the -adrenoceptor antagonist phentolamine did not prevent the apparent catecholamine-mediated increase of P _aCO₂. Conversely, pre-treatment with the -adrenoceptor antagonist sotalol abolished both the activation of the RBC Na⁺/H⁺ antiporter and the associated rise in P _aCO₂, suggesting a causal relationship between the stimulation of RBC Na⁺/H⁺ exchange and the elevation of P _aCO₂. To more clearly establish that elevation of plasma catecholamine levels during severe hypoxia was indeed responsible for causing the elevation of P _aCO₂, fish were exposed to moderate hypoxia (final P _wO₂=60–80 torr) and then injected intraarterially with a bolus of adrenaline to elicit an estimated circulating level of 400 nmol·l^-1 immediately after the injection. This protocol activated RBC Na⁺/H⁺ exchange as indicated by abrupt changes in arterial pH (pHa). In all fish examined, P _aCO₂ increased after injection of exogenous adrenaline. The effects on P _aO₂ were inconsistent, although a reduction in this variable was the most frequent response. Gill ventilation frequency and amplitude were unaffected by exogenous adrenaline. Therefore, it is unlikely that ventilatory changes contributed to the consistently observed rise in P _aCO₂. Pretreatment of fish with sotalol did not alter the ventilatory response to adrenaline injection but did prevent the stimulation of RBC Na⁺/H⁺ exchange and the accompanying increases and decreases in P _aCO₂ and P _aO₂, respectively. These results suggest that adrenergic elevation of P _aCO₂, in addition to the frequently observed reduction of P _aO₂ are linked to activation of RBC Na⁺/H⁺ exchange. The physiological significance and the potential mechanisms underlying the changes in blood respiratory status after addition of endogenous or exogenous catecholamines to the circulation of hypoxic rainbow trout are discussed.Abbreviations P _aCO₂ arterial carbon dioxide tension - P _aO₂ arterial oxygen tension - P _da dorsal aortic pressure - pHa arterial pH - P _wO₂ water oxygen tension - RBC red blood cell - V _f breathing frequency     

Degranulation of eosinophilic granule cells induced by capsaicin and substance P in the intestine of the rainbow trout (Oncorhynchus mykiss Walbaum)

Summary Adult rainbow trout (Oncorhynchus mykiss) were injected intraperitoneally with capsaicin, substance P, serotonin, or a control of saline vehicle or bovine serum albumin (0.5 g/g body weight). Fish were sacrificed 30 min and 1,2 and 4 h post-injection, the gut was dissected out, and a small section of the upper intestine was processed for electron microscopy. A significant proportion of eosinophilic granule cells (EGCs) of the intestine were in close association with non-myelinated neuronal bundles in all fish (4 fish per treatment and time period), but there was no significant difference between treatment or time, suggesting that the association was unaffected by these factors. Close examination of EGC ultrastructure showed that fish treated with capsaicin and substance P exhibited limited degranulation of the EGCs in the stratum compactum and extensive crinophagic-like degranulation in the lamina propria. Cells of the lamina propria contained characteristic multivesicular-like bodies. The degranulation was reminiscent of both mast cell degranulation and endocrine cell crinophagy. EGCs of fish treated with serotonin or a control were unaffected, suggesting that the serotoninergic neurons, believed to be involved in gut motility, were not responsible for degranulation. It is apparent that EGCs of the trout intestine may be under nervous control, as has been demonstrated previously for mammalian mast cells.     

Opsonizing properties of natural antibodies of rainbow trout, Oncorhynchus mykiss (Walbaum)

In order to confirm previous observations in which a protective effect of rainbow trout natural antibodies against furunculosis was suspected, phagocytosis studies wereconducted in vitro , using combinations of rainbow trout sera with high or low levels of natural antibodies and active or inactivated complement as opsonizing factors. Opsonization was observed in all the cases where complement was present, and to a lesser degree with sera containing only natural antibodies. The results confirm the prime importance of the complement system and provide additional evidence for a possible role of natural antibodies in antimicrobial defences.     

Modulation of catecholamine storage and release by the pituitary-interrenal axis in the rainbow trout,Oncorhynchus mykiss

This study examined the effects of pituitary-interrenal hormones on catecholamine storage and release in the rainbow trout Oncorhynchus mykiss. An extract of trout pituitary elicited the release of adrenaline, but not noradrenaline, using an in situ perfusion preparation. A variety of doses of adrenocorticotropic hormone (2–2000 mU) caused the release of both catecholamines in situ which was unaffected by pre-treatment with the ganglion blocker, hexamethonium, or the serotonergic receptor antagonist, methysergide, but was abolished in calcium-free media. Intra-arterial injections of adrenocorticotrophic hormone in vivo caused an elevation of plasma adrenaline but not noradrenaline levels. Injections of cortisol in situ did not elicit catecholamine release. Trout given an intraperitoneal implant of cortisol (50 mg·kg^-1 body weight) had significantly higher plasma cortisol concentrations when compared to controls after 7 days of implantation. Increases in the levels of stored catecholamines were observed in various regions of the kidney and posterior cardinal vein following 3 and 7 days of cortisol treatment. The ability of the chromaffin cells to release catecholamines in response to cholinergic stimulation was assessed in situ after 7 days of treatment. Basal (non-stimulated) adrenaline outflowing perfusate levels were greater in the cortisol-treated fish. Cortisol treatment increased the responsiveness of the catecholamine release process to low doses of the cholinoceptor agonist carbachol. Three or 7 days of cortisol treatment did not alter the in vitro activity of the enzyme phenylethanolamine-N-methyl-transferase. The results of this study demonstrate that interactions within the pituitary-adrenal axis can influence both catecholamine storage and release in the rainbow trout.Abbreviations ACTH adrenocorticotropic hormone - AK anterior third of the kidney - APCV anterior third of the PCV - HPLC high performance liquid chromatography - MK middle third of the kidney - M1 maximum value - MPCV middle third of the PCV - MS222 ethyl-aminobenzoate - P1 pre value - PCA perchloric acid - PCV posterior cardinal vein - PK posterior third of the kidney - PNMT phenylethanolamine-N-methyltransferase - PPCV posterior third of the PCV - rbc red blood cells - SEM standard error of the mean - TK total kidney (i.e. the sum of the AK, MK, and PK) - TPCV total PCV (i.e. the sum of the APCV, MPCV and PPCV)     

Effect of temperature and temperature acclimation on the ryanodine sensitivity of the trout myocardium

The influence of acute temperature change and temperature acclimation on the sensitivity of contracture development to ryanodine were examined in the rainbow trout myocardium using two preparations: in vitro isolated ventricular strips and in situ working perfused hearts. Ryanodine effects in vitro were dependent on test temperature (8 and 18 °C), pacing frequency (0.2–1.5 Hz) and acclimation temperature (8 and 18 °C). At a pacing frequency of 0.2 Hz and a test temperature of 18 °C, ryanodine depressed isometric tension development in ventricular strips both from trout acclimated to 8 and 18 °C but the decrease was significantly greater in strips from 8 °C-acclimated trout. No ryanodine effect was observed in either acclimation group at a test temperature of 8°C. The effect of ryanodine in vitro was reduced or lost at pacing frequencies greater than 0.2 Hz and at 0.6 Hz ryanodine depressed tension development at 18 °C only in strips from 8 °C-acclimated trout. Ryanodine did not affect tension development at stimulation rates above 0.6 Hz in any test group. Likewise, ryanodine did not significantly impair cardiac performance of in situ working perfused heart preparations which operated at intrinsic beat frequencies in excess of 0.6 Hz. These results suggest that the sarcoplamic reticulum calcium release channel of the trout myocardium is expressed but is not functionally involved in beat-to-beat regulation of contractility at either (1) low temperature (8 °C), or (2) at routine physiological heart rate (>0.6 Hz). However, under conditions in which involvement of the sarcoplasmic reticulum is observed (18 °C and a heart rate < 0.6 Hz), prior acclimation to low temperature results in either a greater capacity of the sarcoplasmic reticulum to store releasable calcium or an increase in the amount of calcium that is in releasable form.Abbreviations bm body mass - E-C coupling, excitation-contraction coupling - IVS isometric ventricular strip - SR sarcoplasmic reticulum - TES N-tris[hydroxy-methyl]methyl-2-aminoethane sulfonic acid - WPH in situ working perfused heart     

Developmental changes in the brain-stem serotonergic nuclei of teleost fish and neural plasticity

Summary 1. During early ontogeny, the serotonergic neurons in the brain stem of the three-spined stickleback shows a temporal and spatial developmental pattern that closely resembles that of amniotes.2. However, in the adult fish, only the midline nuclei of the rostral group (dorsal and median raphe nuclei) and the dorsal lateral tegmental nucleus are consistently serotonin-immunoreactive (5-HTir), whereas the groups of the upper and lower rhombencephalon (raphe pontis, raphe magnus, and raphe pallidus/obscurus nuclei) are variable and, when present, contain relatively small numbers of 5-HTir neurons.3. Using specific antisera against tryptophan 5-hydroxylase and aromaticl-amino acid decarboxylase, we have shown that the lateral B9 group and the groups of the upper and lower rhombencephalon are consistently present in adult sticklebacks. The results are discussed in relation to other known instances of neurotransmitter plasticity or transient neurotransmitter expression in teleost fish.4. While there are several instances of transient expression of neurotransmitter markers by discrete neuronal populations, there is so far no evidence of changes from one neurotransmitter phenotype to another in the brain of teleost fish. However, there are indications of plasticity of expression of catecholamines and indoleamines, and their respective synthesizing enzymes, as reflected in age-dependent changes and variation between individuals of different physiological status.5. As the brain grows continuously in teleost fish, and new neurons are added from proliferative regions, synaptic connections may be expected to undergo remodeling in all brain regions throughout life. Thus, the teleostean brain may be considered a suitable model for experimental studies of different aspects of neural plasticity.