SEROTONIN AS A REGULATOR OF HYPOTHALAMIC-PITUITARY-INTERRENAL ACTIVITY IN TELEOST FISH

Evidence for the presence of a serotonin(1A), (5-HT1A) receptor subtyp e in the salmonid fish brain has recently been presented. In the prese nt study the potent 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propyla mino)-tetralin (8-OH-DPAT) was tested for its effect on plasma cortiso l concentrations in rainbow trout (Oncorhynchus mykiss). Blood was sam pled and 8-OH-DPAT administered through a catheter in the dorsal aorta . Thirty minutes after the injection of 40 mu g of 8-OH DPAT/kg, plasm a cortisol levels had increased from 12 to 149 ng/ml, whereupon they f ell, reaching baseline levels after 4 h. The effect of 1-40 mu g 8-OH- DPAT/kg on plasma cortisol concentrations was dose-dependent. The resu lts lends further support to the hypothesis that the brain serotonergi c system plays a key role in integrating autonomic, behavioral and neu roendocrine stress-responses in fish as well as mammals, suggesting th at not only the structural and biochemical organization, but also the function of the serotonergic system has been conserved during vertebra te evolution. (C) 1997 Elsevier Science Ireland Ltd.