Article

Glucocorticoid receptors are involved in the regulation of pulsatile urea excretion in toadfish.

Department of Biology, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
Journal of Comparative Physiology B (Impact Factor: 2.53). 12/2004; 174(8):649-58. DOI: 10.1007/s00360-004-0456-y
Source: PubMed

ABSTRACT The objectives of this study were to characterize the pattern of pulsatile urea excretion in the gulf toadfish in the wake of exogenous cortisol loading and to determine the receptors involved in the regulation of this mechanism. Toadfish were fitted with indwelling arterial catheters and were infused with isosmotic NaCl for 48 h after which fish were treated with cortisol alone, cortisol + peanut oil, cortisol + RU486 (a glucocorticoid receptor antagonist) or cortisol + spironolactone (a mineralocorticoid receptor antagonist). Upon cortisol loading, fish treated with cortisol alone, cortisol + oil or cortisol + spironolactone experienced a two- to threefold reduction in pulsatile urea excretion. This reduction was due to a decrease in urea pulse size with no effect on pulse frequency compared to values measured during the control NaCl infusion period. In addition, these fish showed an increase in plasma urea concentrations upon treatment. These apparent effects of cortisol treatment were abolished in fish treated with cortisol + RU486. In contrast, these fish showed an increase in pulsatile urea excretion mediated by a twofold increase in pulse size with no change in frequency. Likewise, fish treated with cortisol + RU486 showed a significant decrease in plasma urea concentrations over the course of the experiment. The findings of this study indicate that high levels of cortisol reduce pulsatile urea excretion by decreasing pulse size. In addition, it appears that glucocorticoid receptors and not mineralocorticoid receptors are involved in the regulation of the toadfish pulsatile urea excretion mechanism.

Download full-text

Full-text

Available from: M. Danielle Mcdonald, Jun 29, 2015
0 Followers
 · 
88 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cooperation often involves a conflict of interest. This is particularly true in situations where one individual seeks out a service but cannot properly control the quality of the service given by the partner who would gain from defecting. An example is cleaning mutualism involving the bluestreak cleaner wrasse (Labroides dimidiatus) and its reef-fish 'clients'. These cleaners may reduce the stress experienced by their clients by removing parasites; however they occasionally cheat clients (i.e. defect) by eating mucus and other living tissues. Here we present experimental support for the hypothesis that stress responses increase the motivation for clients to seek out such risky asymmetric interactions. We manipulated the stress response by blocking glucocorticoid receptors with the antagonist RU486 in a species that is a regular visitor of cleaner fish, the lined bristletooth (Ctenochaetus striatus). Field observations 1 week after treatment with RU486 showed that antagonist treatment led to a reduction in cleaning duration compared to control treatment. This was not explained by a general effect on client behavior as intraspecific social behavior appeared unaffected. We propose that antagonist treatment reduced stress responses to the presence of ectoparasites, which in turn reduced the client's perception of benefits from seeking out cleaning interactions. The results demonstrate a hitherto overlooked variable role of stress and stress responses on cooperative behavior.
    Hormones and Behavior 01/2012; 61(1):37-43. DOI:10.1016/j.yhbeh.2011.09.013 · 4.51 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gulf toadfish, Opsanus beta, are one among a group of unusual teleosts that excrete urea as their predominant nitrogen end product in response to stressful conditions. Under conditions of crowding or confinement, fasted toadfish excrete the majority of their nitrogen waste in large pulses of urea (>90% of total nitrogen) lasting up to 3 h. An earlier study demonstrated that cortisol has an inhibitory influence on urea pulse size. The present study tested the hypothesis that cortisol mediates changes in urea pulse size in ureotelic toadfish through the glucocorticoid receptor (GR) and not the mineralocorticoid receptor (MR). In vivo pharmacological investigations were used to manipulate the corticosteroid system in crowded toadfish, including experimentally lowering plasma cortisol levels by the injection of metyrapone, blocking cortisol receptors through exposure to either RU-486 (GR antagonist) and spironolactone (MR antagonist), or through exogenous infusion of the tetrapod mineralocorticoid aldosterone (tetrapod MR agonist). The data demonstrate that lowering the activity of cortisol, either by inhibiting its synthesis or by blocking its receptor, resulted in a two- to threefold increase in pulse size with no accompanying change in pulse frequency. Treatment with spironolactone elicited a minor ( approximately 1.5-fold) reduction in pulse size, as did aldosterone treatment, suggesting that the anti-mineralocorticoid spironolactone has an agonistic effect in a piscine system. In summary, the evidence suggests that urea transport mechanisms in pulsing toadfish are upregulated in response to low cortisol, mediated primarily by GRs, and to a lesser extent MRs.
    Journal of Experimental Biology 06/2009; 212(Pt 12):1849-58. DOI:10.1242/jeb.026997 · 3.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A Power Distribution Unit (PDU) is being developed by The Johns Hopkins University Applied Physics Laboratory for the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft that will orbit the planet Mercury for one Earth year to complete the global mapping and the detailed characterization of the planet's exosphere, magnetosphere, surface, and interior. The PDU contains the circuitry for the spacecraft pyrotechnic firing control, power distribution switching, load current and voltage monitoring, fuses, external relay switching, reaction wheel relay selects, and power system relays. It also supports the Inertial Measurement Unit (IMU) reconfiguration, Integrated Electronic Module (IEM) select relays, solar array drives, propulsion thruster firing control, and propulsion latch valve control. To enable the mission to reach the distant planet, significant weight reduction for all spacecraft electronics must be achieved. This requirement has led to an advanced electronic packaging design that begins with component selection, printed wiring board design with very small feature sizes, and a compact interconnection scheme. The significant challenge in the packaging design of the PDU is how to implement state-of-the-art technologies to minimize system weight and meet the stringent reliability required by the MESSENGER power system. This paper will describe the detailed electronic packaging design of the PDU, including the use of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) devices instead of conventional mechanical relays, high-density printed wiring board designs with blind and buried vias, and a modular packaging design to achieve significant weight reduction.
    Digital Avionics Systems Conference, 2002. Proceedings. The 21st; 02/2002