Biomedical subjects

R J Balment

Publications and source records attributed to R J Balment.

At least 37 records · Page 2Linked to original sources

PubMed2001

Bursting properties of caudal neurosecretory cells in the flounder Platichthys flesus, in vitro.

Bursting activity in type 1 Dahlgren cells was studied using intra- and extracellular recording from an in vitro preparation of the caudal neurosecretory system of the euryhaline flounder. 45% of cells showed spontaneous bursts of approximately 120s duration and 380s cycle period. Similar bursts were triggered by short duration (<5s) depolarising or hyperpolarising pulses. Cells displayed a characteristic depolarising after potential, following either an action potential with associated afterhyperpolarisation, or a hyperpolarising current pulse. This depolarising after potential was related to a 'sag' potential, which developed during the hyperpolarising pulse. Both the depolarising after potential and the sag potential occurred only in cells at more depolarised (<60 mV) holding potentials. In addition, the amplitude of the depolarising after potential was dependent on the amplitude and the duration of the hyperpolarising pulse. The depolarising after potential following action potentials may provide a mechanism for facilitating repetitive firing during a burst. Extracellular recording revealed similar bursting in individual units which was not, however, synchronised between units. Spontaneous bursting activity recorded both intra- and extracellularly was inhibited by application of a known neuromodulator of the system, 5-hydroxytryptamine. This study provides a basis for investigating the relationship between physiological status, Dahlgren cell activity and neuropeptide secretion.

Action Potentials↗

PubMed2000

Cloning of pro-vasotocin and pro-isotocin cDNAs from the flounder Platichthys flesus; levels of hypothalamic mRNA following acute osmotic challenge.

Sequences coding for pro-vasotocin and pro-isotocin have been identified by screening a flounder (Platichthys flesus) hypothalamic cDNA library. The 1074-bp proVT and 727-bp proIT sequences contain a signal peptide and hormone, connected to a neurophysin by a Gly-Lys-Arg sequence. Both sequences also have an elongated carboxyl-terminal with a leucine-rich core resembling copeptin but lacking the amino terminal Arg residue. The levels of pro-vasotocin and pro-isotocin mRNA in the hypothalamus were measured concomitantly with pituitary AVT content and plasma AVT concentration following acute transfer of fish between freshwater and seawater. Three days after transfer from seawater to freshwater there appears to be a down regulation of the AVT hormone system with a fall in hypothalamic pro-vasotocin mRNA levels, an increase in pituitary AVT content, and a fall in plasma levels, but these changes did not achieve statistical significance compared to controls. No change in the AVT system was detected 3 days following the transfer of fish from freshwater to seawater. Hypothalamic isotocin mRNA levels did not change following hypo- or hyperosmotic challenge.

Amino Acid Sequence↗

PubMed2000

Renal electrolyte and fluid handling in the rat following chloroquine and/or ethanol administration.

We postulated that chloroquine and/or ethanol affect plasma arginine vasopressin (AVP) concentrations to alter renal function. Therefore, we studied the effects of chloroquine and/or ethanol on plasma AVP concentrations and fluid, urinary Na(+) and K(+) outputs in separate groups of anaesthetized Sprague-Dawley (SD) rats challenged with a continuous jugular infusion of 0.077 M NaCl at 150 microl.min(-1). After a 3-h equilibration period, vehicle, chloroquine (0.06 microg. min(-1)), ethanol (2.4 or 24 microg.min(-1)) or both chloroquine and ethanol were added to the infusate after 1 h (control) for 1 h 20 min (treatment). The animals were switched back to the infusate alone for the final 1 h 40 min recovery periods. Urine flow Na(+) and K(+) excretion rates were determined at 20-min intervals over the subsequent 4-h postequilibration period. Blood was collected from separate groups of animals at the end of treatment period or equivalent time for control animals for measurement of plasma aldosterone and AVP concentrations by radioimmunoassay. Simultaneous chloroquine and ethanol infusion significantly (p < 0.01) increased plasma chloroquine concentrations in an ethanol dose-dependent manner by comparison with animals administered chloroquine alone. Chloroquine infusion alone (0.06 microg.min(-1)) and/or ethanol (2.4 or 24 microg.min(-1)) elevated plasma AVP concentrations from 9.73 +/- 1.64 fmol.l(-1) in control rats to 15.65 +/- 2.49 fmol.l(-1), 17. 39 +/- 4.21 fmol.l(-1), and 33.87 +/- 6.18 fmol.l(-1), respectively. Separate administration of chloroquine or ethanol at low dose rates increased urinary Na(+) excretion rates. We conclude that the impairment of renal electrolyte handling associated with chloroquine administration may be exacerbated by ethanol.

Animals↗

PubMed2000

Effects of ethanol on the changes in renal fluid and electrolyte handling and kidney morphology induced by long-term chloroquine administration to rats.

This study investigated the effects of long-term chloroquine and ethanol administration on renal fluid and electrolyte handling and kidney structure. Male Sprague-Dawley rats were orally administered with chloroquine diphosphate (20 microg kg(-1) bw) and/or ethanol (1.6 g kg(-1) bw) every third consecutive day for 4 weeks. Urine volume and total urinary outputs of Na+ and K+ were determined from 24-h samples. For detailed renal studies, rats were subsequently anaesthetised and challenged with a continuous jugular infusion of 0.077 M NaCl at 150 microl min(-1) 24 h after the last treatment. After a 3-h equilibration period, urine flow, Na+ and K+ excretion rates were determined over a 4-h period. Plasma concentrations of AVP and aldosterone were measured in unanaesthetised rats and in anaesthetised rats after hypotonic saline infusion. In separate groups, the rats were anaesthetised with an overdose of ether after 4 weeks of treatment and part of the right kidney was quickly collected and routinely processed for light microscopy. Chloroquine decreased Na+ excretion and increased plasma aldosterone concentrations in anaesthetised rats. Ethanol alone did not alter urinary Na+ outputs or aldosterone levels. Combined chloroquine and ethanol increased renal Na+ excretion, but did not affect plasma aldosterone levels. In unanaesthetised animals all treatments increased aldosterone levels by comparison with control rats. Urinary Na+ excretion was decreased by separate administration of either chloroquine or ethanol, but increased by combined treatment. Microscopic studies showed that concurrent chloroquine and ethanol administration induced extensive damage of the proximal tubule and collecting ducts cells. The results of this study suggest that alcohol consumption and chloroquine administration could result in diminished renal function possibly due to alteration of renally active hormones or kidney morphology.

Aldosterone↗

PubMed2000

Chloroquine inhibits arginine vasopressin production in isolated rat inner medullary segments induced cAMP collecting duct.

Previous studies showed that acute chloroquine administration increases plasma arginine vasopressin (AVP) concentration in the rat without influencing urine flow rate. The present study was designed to investigate whether chloroquine inhibits the AVP-induced cAMP production that mediates the antidiuretic effects of vasopressin. Single inner medullary collecting duct (IMCD) segments were pre-incubated at 35 degrees C for 10 min followed by 4 min at 37 degrees C with combinations of AVP and/or chloroquine with 1 mM 3-isobutyl-I-methylxanthine (IBMX) and cAMP concentrations were measured by radioimmunoassay. To establish the possible site of interference in cAMP production IMCD segments were incubated in the presence of chloroquine and forskolin. Chloroquine at concentrations ranging from 10(-9) M to 10(-6) M did not affect cAMP production by comparison with control. However, AVP (10(-8) M) and forskolin (10(-6) M) significantly (p < 0.01) increased cAMP accumulation. Chloroquine at all concentrations significantly suppressed the AVP stimulated cAMP production (e.g., chloroquine (10(-8) M) + AVP (10(-8) M) 41 +/- 12 fmol/4 mm (n = 9 tubules) vs. AVP (10(-8) M) alone 82 +/- 9 fmol/4 min/mm (n = 37 tubules). Chloroquine at all concentrations tested did not have any effect an forskolin-induced cAMP production. The data suggest that chloroquine inhibits the AVP induced cAMP production at the level of hormone/receptor complex. This possibly explains the previously reported lack of the normal antidiuretic responses of AVP in rats following chloroquine administration.

Animals↗

PubMed2000

Altered calbindin mRNA expression and calcium regulating hormones in rat diabetic pregnancy.

Offspring of rats with diabetes mellitus are at risk of reduced calcium and bone mineral content. Altered expression of the maternal calcium binding proteins, calbindin-D(9K) and calbindin-D(28K), which are involved in renal and placental calcium transport, may underlie these problems.We have investigated the effect of diabetes on circulating concentrations of regulatory hormones with respect to calbindin-D mRNA concentrations. Three rat groups were studied; control (CP), streptozotocin-induced diabetic (DP), and insulin-treated diabetic (DPI) pregnant rats. Calbindin-D(9K) and calbindin-D(28K) mRNA abundance in placenta and maternal kidney were measured at days 7, 15, 18 and 21 of gestation, together with serum or plasma concentrations of 1,25 dihydroxyvitamin D(3) (1, 25(OH)(2)D(3)), parathyroid hormone (PTH), PTH-related protein (PTHrP), calcitonin, oestradiol and IGF-I. An increase in placental calbindin-D(9K) mRNA abundance between days 18 and 21 in CP and DPI rats was severely blunted in the DP rats. In contrast, renal calbindin-D(28K) mRNA abundance was greater at days 7, 15 and 18 in DP compared with CP rats, as was calbindin-D(9K) at day 18. Calcitonin concentrations showed no differences between the groups, and both PTH and IGF-I were reduced over the first half of gestation, unlike the calbindins. In contrast, the concentrations of PTHrP and 1,25(OH)(2)D(3) were reduced at term in the DP group compared with the other two groups. Plasma oestradiol concentrations were lower in DP than in CP rats at days 7, 15 and 18, and most striking was the absence in DP rats of the peak of oestradiol seen at day 18 in CP rats. Despite the similarity between changes in placental calbindin mRNA and 1,25(OH)(2)D(3), previous work has shown placental calbindin-D(9K) regulation to be vitamin-D-independent. These studies produce suggestive evidence, therefore, that PTHrP and oestradiol may be involved in the altered calbindin-D expression by kidney and placenta in rat diabetic pregnancy.

Animals↗

PubMed2000

The caudal neurosecretory system: control and function of a novel neuroendocrine system in fish.

The caudal neurosecretory system (CNSS) of fish was first defined over 70 years ago yet despite much investigation, a clear physiological role has yet to be elucidated. Although the CNSS structure is as yet thought to be confined to piscine species, the secreted peptides, urotensins I and II (UI and UII), have been detected in a number of vertebrate species, most recently illustrated by the isolation of UII in humans. The apparent importance of these peptides, suggested by their relative phylogenetic conservation, is further supported by the complex control mechanisms associated with their secretion. The CNSS in teleosts is known to receive extensive and diverse innervation from the higher central nervous system, with evidence for the presence of cholinergic, noradrenergic, serotonergic, and peptidergic descending inputs. Recent observations also suggest the presence of glucocorticoid receptors in the flounder CNSS, supporting previous evidence for a possible role as a pituitary-independent mechanism controlling cortisol secretion. The most convincing evidence as to a physiological role for the CNSS in fish has stemmed from the direct and indirect influence of the urotensins on osmoregulatory function. Recent advances allowing the measurement of circulating levels of UII in the flounder have supported this. In addition, there is evidence to suggest some seasonal variation in peptide levels supporting the notion that the CNSS may have an integrative role in the control of coordinated changes in the reproductive, osmoregulatory and nutritional systems of migratory euryhaline species.

Amino Acid Sequence↗

PubMed1999

A homologous radioimmunoassay for the measurement of urotensin II in the euryhaline flounder, Platichthys flesus.

A sensitive and specific homologous radioimmunoassay (RIA) has been developed to measure tissue and circulating levels of the fish caudal neurosecretory system neuropeptide, urotensin II (UII), in the euryhaline flounder Platichthys flesus. A polyclonal antiserum was raised against flounder UII in rabbit; UII-125I was produced by the iodogen method and purified by HPLC. Antiserum specificity to flounder UII was demonstrated through lack of cross-reactivity with several small peptides and parallelism with standard curves for serial dilutions of UII in plasma and urophysial extracts. Biological activity of the peptide measured by UII RIA was confirmed by bioassay. Plasma intra- and interassay coefficients of variation were 9 and 18% (n = 5 and n = 3), respectively, nonspecific binding constituted 4.6% (+/-1.42%, n = 8) of total counts, and the limit of RIA detectability was estimated as 1.5 x 10(-16) M UII/assay tube. Plasma samples were subject to a reversed-phase liquid chromatography purification protocol which had an extraction efficiency of 63% (+/-10%, n = 6) and showed consistent recovery of UII over a range of plasma volumes and peptide concentrations. Plasma UII concentrations in seawater (SW)-adapted flounder (3.80 +/- 0.77 x 10(-11) M, n = 7) were significantly higher than those in freshwater (FW)-adapted fish (1.10 +/- 0.15 x 10(-11) M, n = 7). This variation coincided with differences in plasma osmolality and Na+ levels. No differences were found, however, between urophysial UII concentrations in SW-adapted (3.71 +/- 1.78 x 10(-10) M UII/gland, n = 7) and FW-adapted (2.53 +/- 1.33 x 10(-10) M UII/gland, n = 7) flounder.

Adaptation, Physiological↗

PubMed1999

Evolution and physiology of the corticotropin-releasing factor (CRF) family of neuropeptides in vertebrates.

Corticotropin-releasing factor (CRF), urotensin-I, urocortin and sauvagine belong to a family of related neuropeptides found throughout chordate taxa and likely stem from an ancestral peptide precursor early in metazoan ancestry. In vertebrates, current evidence suggests that CRF on one hand, and urotensin-I, urocortin and sauvagine, on the other, form paralogous lineages. Urocortin and sauvagine appear to represent tetrapod orthologues of fish urotensin-I. Sauvagine's unique structure may reflect the distinctly derived evolutionary history of the anura and the amphibia in general. The physiological actions of these peptides are mediated by at least two receptor subtypes and a soluble binding protein. Although the earliest functions of these peptides may have been associated with osmoregulation and diuresis, a constellation of physiological effects associated with stress and anxiety, vasoregulation, thermoregulation, growth and metabolism, metamorphosis and reproduction have been identified in various vertebrate species. The elaboration of neural circuitry for each of the two paralogous neuropeptide systems appears to have followed distinct pathways in the actinopterygian and sarcopterygian lineages of vertebrates. A comparision of the functional differences between these two lineages predicts additional functions of these peptides.

Amino Acid Sequence↗

PubMed1999

Renal function in chronically catheterized conscious diabetic rats using constant and servo-controlled infusion.

1. Infusion experiments were performed on chronically catheterized conscious rats to assess kidney function before and after the induction of diabetes mellitus with streptozotocin. 2. Two infusion regimens were used, a conventional constant-infusion protocol and a novel computer-driven, servo-controlled fluid replacement technique. The latter enables body fluid status to be maintained throughout a study occasion by servo-controlled replacement of spontaneous urinary fluid losses. 3. The chronically catheterized conscious rat infused using a servo-controlled system appears to be the optimum model for a study of diabetic renal function. The conscious preparation circumvents problems associated with anaesthesia and acute surgery. The servo-controlled infusion protocol maintains the altered fluid status of the diabetic condition. Both hyperfiltration and polyuria, characteristics of human diabetes often absent in anaesthetized and/or constantly infused diabetic rats, were seen in all conscious servo-controlled diabetic animals. 4. The new regimen enables a more accurate assessment of renal function in experimental diabetes than with previous protocols. It should prove useful in future studies, particularly those assessing the role of anti-diabetic drugs on the kidney.

Animals↗

PubMed1999

Separate receptors mediate oxytocin and vasopressin stimulation of cAMP in rat inner medullary collecting duct cells.

The two neurohypophysial hormones arginine vasopressin (AVP) and oxytocin have actions in the inner medullary collecting duct (IMCD) where both peptides induce an increase in cAMP accumulation. The present study has employed a novel IMCD cell line to determine whether these two hormones induce cAMP accumulation via common or separate receptors, and to characterize the potential receptors responsible. Equal volumes of vehicle (150 mM NaCl) or hormone/antagonist solutions were added to aliquots of 10(4) IMCD cells in the presence of 10(-3) M 3-isobutylmethylxanthine (IBMX) and incubated at 37 degrees C for 4 min. cAMP levels were determined by radioimmunoassay and protein concentration by Bradford assay. Both AVP and oxytocin elicited dose-dependent increases in cAMP generation, though oxytocin was less potent than AVP (EC50 = 1.6 x 10(-8) M vs. 7.4 x 10(-10) M). AVP at 10(-8) M and oxytocin at 10(-8) M, concentrations sufficient to elicit near-maximal cAMP accumulation, resulted in cAMP levels of 73.4 +/- 1.7 and 69.0 +/- 3.3 pmol (mg protein)-1 (4 min)-1, respectively (n = 10), compared with the vehicle-treated basal value of 37.7 +/- 2.2 pmol (mg protein)-1 (4 min)-1 (P < 0.001, n = 10). Combined AVP (10(-8) M) and oxytocin 10(-6) M) resulted in cAMP accumulation of 63.8 +/- 3.1 pmol (mg protein)-1 (4 min)-1 (n = 10), which was not significantly different from the effect of oxytocin alone, but slightly less than that for AVP alone (P < 0.05). A submaximal concentration of AVP (10(-10) M) induced cAMP accumulation of 48.6 +/- 2.5 pmol (mg protein)-1 (4 min)-1 (P < 0.01 compared with basal level of 34.9 +/- 2.4 pmol (mg protein)-1 (4 min)-1, n = 10), which was blocked in the presence of a vasopressin V2 receptor antagonist (10(-7) M OPC-31260) but not by the oxytocin receptor antagonist (10(-6) M [Pen1,pMePhe2, Thr4,Orn8]oxytocin) (36.3 +/- 6.1 and 45.1 +/- 1.3 pmol (mg protein)-1 (4 min)-1 respectively, P < 0.05, n = 10). A submaximal concentration of oxytocin (10(-7) M) induced a cAMP accumulation of 45.8 +/- 1.8 pmol (mg protein)-1 (4 min)-1 (n = 10), which was reduced by addition of 10(-6) M oxytocin antagonist (36.3 +/- 2.1 pmol (mg protein)-1 (4 min)-1, P < 0.05, n = 10), whereas co-incubation with 10(-6) M of the V2 receptor antagonist had no effect (43.2 +/- 1.3 pmol (mg protein)-1 (4 min)-1, n = 10). These results indicate that AVP and oxytocin induce cAMP accumulation from a common ATP pool in IMCD cells, and that separate vasopressin V2 and oxytocin receptor systems are involved, perhaps coupled to a common adenylate cyclase system.

Animals↗

PubMed1999

Vascular, renal, and endocrine responses to low-dose atrial natriuretic peptide in the fluid-balanced New Zealand genetically hypertensive rats with and without endogenous arginine vasopressin.

In hypertension, the relationship between atrial natriuretic peptide (ANP) and vasopressin (AVP) is not yet clear, although their renal actions are effectively autoregulation. To examine the possible interaction further, the responses to ANP infusion (75 ng x min (-1), i.v.) have been investigated in both hypertensive and normotensive AVP-replete (HT and NT) and AVP-deficient (HTDI and NTDI) rats. This study aimed to assess the renal function and the plasma hormone concentrations of AVP, angiotensin II (AII), ANP, aldosterone, and corticosterone in the conscious, chronically catheterized, fluid-balanced rats, and to examine the cardiovascular, renal, and endocrine responses to a constant infusion of a low-dose ANP. Data gained from the present study showed, for the first time, the hormone profile, plasma electrolyte composition, and detailed renal function of the servo-controlled, fluid-balanced rats. The similarities of plasma electrolyte composition between servo-controlled and untreated rats indicated that the servo-controlled fluid replacement technique maintained the differences between the strains and maintained body fluid balance during the experimental periods. Following ANP administration, there were no changes in glomerular filtration rate (GFR) in all groups, but an enduring diuresis and natriuresis were observed in HT and NT, which were milder in HTDI rats. However, the hypotensive effect of ANP was of a similar magnitude in all rat strains. HTDI rats exhibited an inhibition of the renin-angiotensin system (RAS), which may have participated in the reduced mean arterial blood pressure (MAP) and natriuresis observed in these rats. The renal actions of ANP appear to rely upon renal tubular events, as indicated by increased fractional electrolyte excretions in the AVP-replete rats. This study highlights the importance of AVP to the profile of the renal actions of ANP in normal rats.

Animals↗

PubMed1998

Native urotensins influence cortisol secretion and plasma cortisol concentration in the euryhaline flounder, platichthys flesus.

Adrenocorticotrophic hormone (ACTH) and flounder urotensins I and II (UI and UII) stimulate cortisol secretion of isolated interrenal/head kidney preparations of seawater (SW)-adapted flounder. UI and UII at concentrations of 10(-6) and 10(-7) M, respectively, increased cortisol secretion when acting on SW-derived interrenal but did not affect cortisol secretion in tissue derived from freshwater (FW) fish. Combined UI and UII had no synergistic or additive steroidogenic action, but either 10(-7) M UI or 10(-7) M UII in combination with ACTH produced a very marked, additive, or synergistic steroidogenic response, most apparent on interrenal derived from FW fish. These results suggest that urotensins enhance the steroidogenic action of ACTH in flounder. In all cases, significant steroidogenesis was apparent within 1 h postperifusion of ligands. In SW-adapted flounder intraarterial infusion of UII in vivo caused a concentration-dependent increase in plasma cortisol concentration within 1 h after infusion, while after 5 x 10(-6) M UI infusion a similar trend was evident but this did not achieve statistical significance. The data suggest that the caudal neurosecretory system may control interrenal cortisol secretion, to modulate cortisol secretion independently of the hypophysial axis, perhaps in response to specific stress-induced or osmoregulatory challenge.

Adrenocorticotropic Hormone↗

PubMed1998

Indices of carbohydrate and lipid metabolism in vasopressin-replete and -deficient New Zealand genetically hypertensive rats.

Indices of carbohydrate and lipid metabolism were investigated in male New Zealand genetically hypertensive and normotensive rats. Cross-breeding of male rats of these strains with female Brattleboro diabetes insipidus rats also provided the opportunity to examine the metabolic impact of vasopressin and its deficiency in hypertensive and normotensive rats. Hypertensive and normotensive rats, with or without diabetes insipidus, were fasted for 24 h, exsanguinated and their blood/plasma analysed for various indices of carbohydrate and lipid metabolism. Whilst each group of rats maintained fasted normoglycemia, hypertensive rats, with or without vasopressin-deficiency, were hypoinsulinaemic relative to normotensive counterparts. Moreover, hypertensive or normotensive vasopressin-deficient rats were hypoinsulinaemic relative to vasopressin-replete counterparts. In vasopressin-replete rats, the apparently improved insulin sensitivity in hypertension was associated with significant falls in plasma glucagon, triglycerides and total cholesterol. Finally, normotensive vasopressin-deficient rats were hypoglucagonaemic relative to the vasopressin-replete group. These data demonstrate that independent of vasopressin status, hypertension in the New Zealand strain and the diabetes insipidus hybrid was associated with improved insulin sensitivity. However, endogenous vasopressin exercises an influential role in carbohydrate and lipid metabolism in normotensive rats.

Animals↗

PubMed1998

Bone mineral density and composition in rat pregnancy: effects of streptozotocin-induced diabetes mellitus and insulin replacement.

A disturbed calcium homeostasis characterizes diabetic pregnancy. This study documents changes in bone mineral composition in diabetic pregnant rats and examines the effect of insulin replacement. Control pregnant (CP), diabetic pregnant (DP) and insulin-treated DP (DPi) rats were assessed for femoral calcium and magnesium content, bone mineral density (BMD) and the ratio of hypertrophic to maturing and proliferative cells in the femoral growth plate. DP rats showed a significantly (P < 0.01) lower body weight, femoral weight and length than CP rats. Femoral calcium and magnesium content was also significantly (P < 0.05) lower in DP rats, as was ash weight. When calcium and magnesium were normalized for ash weight no significant differences were apparent. A significantly (P < 0.05) lower total BMD at the distal femur was seen in DP rats. This comprised a significantly (P < 0.01) lower trabecular BMD with no significant change in cortical BMD. A significantly (P < 0.05) higher ratio of hypertrophic to maturing and proliferative cells of the femoral growth plate was evident in DP animals. DPi rats showed normal blood glucose concentrations and femoral growth plate histology. DPi rats also showed normal femoral weight and length but only partially restored femoral ash weight and mineral content. Insulin failed to normalize total or trabecular BMD. Diabetes mellitus clearly has a marked effect on bone growth and mineral content in pregnancy which may be relevant to overall calcium homeostasis. The lower bone growth, bone calcium content and trabecular BMD may be unfortunate consequences of the marked hypercalciuria reported elsewhere in diabetes and may serve to maintain normocalcaemia in the disease.

Animals↗

PubMed1997

Changes in plasma arginine vasotocin (AVT) concentration and dorsal aortic blood pressure following AVT injection in the teleost Platichthys flesus.

Dorsal aortic blood pressure and plasma arginine vasotocin (AVT) concentrations have been assessed in free swimming, chronically cannulated flounder following AVT injection. Intraarterial AVT at doses of 4.76 x 10(-12) mol.kg-1 and greater caused a biphasic change in blood pressure (an initial fall followed by a sustained pressor response). Doses above 4.76 x 10(-12) mol.kg-1 were associated with plasma AVT concentrations (20 min after injection) 2-3 orders of magnitude greater than the physiological range and must be considered pharmacological. Injection of the lowest pressor AVT dose (4.76 x 10(-12) mol.kg-1), 20 min after injection, increased plasma AVT concentrations to 23.4 +/- 6.1 fmol x ml-1. This increase is close to plasma AVT concentrations recently reported in untreated fish; however, in the initial period after injection plasma levels were calculated to be considerably higher than the physiological range. These results confirm that AVT is pressor in flounder but suggest that the pressor response may occur only at circulating AVT levels above the normal physiological range. The biphasic response to AVT and the differing responses to mammalian V1 and V2 type receptor agonists in the current work suggests that AVT may contribute to regional blood flow distribution in teleosts rather than blood pressure regulation.

Animals↗

PubMed1997

Inhibitory effect of 5-hydroxytryptamine receptor activation on caudal neurosecretory cells of the flounder, Platichthys flesus.

Immunocytochemical evidence suggests that the neuroendocrine Dahlgren cells of the teleost caudal neurosecretory system (CNSS) are innervated by descending serotonergic fibres. However, the modulatory effect(s) of 5-hydroxytryptamine (5-HT) on the activity of the CNSS are not known. The present study investigates the effect of superfusion of 5-HT and the selective 5-HT1 receptor agonist 5-carboxamidotryptamine (5-CT) on the electrophysiological properties of Dahlgren cells recorded intracellularly in an isolated CNSS preparation from the flounder. Superfusion of 5-HT (10(-7)-10(-3) M) caused a concentration-dependent, reversible hyperpolarization of the resting membrane potential (Em) of cells previously identified as 'Type 1' (putative urotensin I-secreting) cells (control = -63.5 +/- 1.5 mV; 10(-4) M 5-HT = -95.0 +/- 0.9 mV, n = 6, P<0.01). The EC50 was 7.6 +/- 4.1 microM (n = 6). Hyperpolarization resulted in a reduction or cessation of firing of these cells, suggesting an inhibitory role for the serotonergic input to the CNSS. Hyperpolarization was accompanied by a concomitant decrease in the membrane input resistance (control = 16.6 +/- 2.8 Momega; 10(-4) M 5-HT = 6.4 +/- 1.3 MD; n = 6, P<0.05) and time constant (control = 60.3 +/- 13.1 ms; 10(-4) M 5-HT = 16.0 +/- 4.4 ms, n = 6, P < 0.05). These effects were mimicked by the superfusion of much lower concentrations of 5-CT (EC50 = 47.1 +/- 7.1 nM, n = 4) suggesting that they are possibly mediated by a 5-HT1 receptor subtype, if the teleost 5-HT1 receptor has a markedly higher affinity for 5-CT than 5-HT, in common with mammalian 5-HT1 receptors. In contrast to the findings in Type 1 cells, cells identified as 'Type 2' (putative urotensin II-secreting) did not respond to either 5-HT or 5-CT, suggesting that the serotonergic input into the CNSS plays no role in the modulation of activity of this sub-population of neuroendocrine cells. Accordingly, these data suggest a functional difference between Type 1 and Type 2 Dahlgren cells, previously differentiated only on electrophysiological criteria and spatial distribution within the CNSS.

Animals↗

PubMed1997

Distribution and expression of glucocorticoid receptor mRNA in the forebrain of the rainbow trout.

The expression and distribution of glucocorticoid receptor mRNA was studied in the forebrain of mature female and immature undifferentiated rainbow trout (Oncorhynchus mykiss) by means of Northern blotting and in situ hybridization. A single mRNA species of 7.5 kb was detected in mRNA polyA+ prepared from the anterior brain. In situ hybridization was carried out using a 35S-labelled riboprobe corresponding to the A/B-domain (between nucleotides 1224 and 1763) of the recently cloned rainbow trout glucocorticoid receptor cDNA. Comparison of adjacent sections hybridized with the sense and antisense probes allowed detection of a specific signal with a similar distribution pattern in all animals studied. In the telencephalon, a specific hybridization was detected in scattered cells of the dorsal telencephalic hemisphere, but the stronger signal was consistently observed in the dorsal nucleus, and to a lesser degree in the ventral nucleus of the ventral telencephalon. Heavy hybridization staining was consistently observed in all subdivisions of the preoptic nucleus and the nucleus lateralis tuberis, which are the main hypophysiotrophic regions in fish. A weaker signal was detected in the nucleus anterioris periventricularis, nucleus suprachiasmaticus and thalamic region. The presence of a strong signal in virtually all magnocellular neurons of the nucleus preopticus, known for producing vasotocin, isotocin and corticotropin-releasing factor favors a direct function of cortisol in regulating its own secretion.

Animals↗