Tomasz Mikolajczyk

Attempts to induce an LH surge and ovulation in common carp (Cyprinus carpio L.) by differential application of a potent GnRH analogue, azagly-nafarelin, under laboratory, commercial hatchery, and natural conditions

Abstract The study was performed in order to try to provoke the gonadotropin wave and ovulation in common carp using a potent GnRH analogue, azagly-nafarelin (AZAGLY), without the use of dopamine (DA) antagonists. Different doses, routes of delivery, and injection protocols were applied, as well as different experimental conditions (laboratory, hatchery, and natural). It has been shown that the best and the simplest way of AZAGLY administration was by intraperitoneal injection. Despite dose (40 or 80 μg/kg body weight) and number of injections (one or two), maximal plasma carp-luteinizing hormone (cLH) concentrations never exceeded 40–50 ng/ml. There was no priming effect on final plasma cLH concentrations. Using different treatment protocols, it was possible to obtain 40–60% ovulated females in laboratory as well as hatchery conditions. However, time of ovulation after AZAGLY treatment in some cases was less compressed in comparison with Ovopel-treated (a local commercial product, containing a GnRH analogue plus the dopamine antagonist, metoclopramide) fish. Egg quality was not altered by AZAGLY treatment. With natural spawning, in unfavourable thermal conditions, AZAGLY treatment induced spawning in a limited number of females. It is postulated that, if antidopaminergic drugs are ever banned from use in aquaculture, AZAGLY treatment alone can be considered as an alternative method of inducing ovulation in cyprinid fish for artificial spawning.

Seasonal short-term effects of naltrexone on LH secretion in male carp (Cyprinus carpio L.)

In order to evaluate the influence of the season (the stage of gonad maturity) on the modulatory role of endogenous opioid peptides in LH secretion in fish, sexually mature male carp (Cyprinus carpio L.) were intravenously injected with naltrexone-opioid receptor antagonist (5 or 50 microg kg(-1)) in the period of natural spawning (June) or gonad recrudescence (December). Moreover, the possible involvement of the dopaminergic system was studied in fish pre-treated with pimozide (dopamine receptor antagonist) and in intact fish. Blood samples were taken every minute, up to 10 min after naltrexone injection. In June, naltrexone significantly lowered LH levels in comparison to saline injected males. In December, there were no differences between saline and naltrexone-injected carps. In fish pre-treated with pimozide, neither in June nor in December were any significant differences in LH levels between control group and the groups injected with naltrexone found. The results showed that, in male carp, LH secretion under the influence of naltrexone depends on the stage of gonad maturity what suggests that the feedback of gonadal steroids on LH release could be mediated by the endogenous opioids. The role of dopamine in these processes is also discussed.

A presumptive role for GABA in the stimulatory effects of desgly10, [D-AlA6]-LHRH-ethylamide and pimozide on the gonadotropin release in carp

To investigate the effect of endogenous gamma-aminobutyric acid (GABA) on the blood maturating gonadotropin (GtH) levels, or to study its interaction with pimozide (dopamine antagonist) and a luteinizing hormone-releasing hormone analog (LHRH-a), sexually mature male and female carps were treated with drugs that may either inhibit GABA biosynthesis or GABA degradation. In females the irreversible inhibitor of GABA-transaminase, gamma-vinyl GABA (GVG), which was to increase the endogenous GABA-ergic tone, had no influence on GtH release. On the other hand, the increased GtH response to the combination of pimozide (PIM) and LHRH-a was clearly enhanced by the administration of 3-mercaptopropionic acid (MPA), an inhibitor of the rate limiting enzyme of GABA-biosynthesis. In males the GABA-ergic compound, valproic acid (DPA) decreased LHRH-a stimulated GtH levels. In male carps that received PIM to diminish the dopaminergic inhibition of GtH release, the spermiating response to LHRH-a was increased by administration of MPA. These data suggest that GABA interacts with the action of dopamine and the gonadotropin releasing hormone (GnRH) on the release of GtH.

Modified absorption of sGNRH-a following rectal and oral delivery to common carp, Cyprinus carpio L.

Abstract The present study compare oral and rectal delivery routes of a salmonid gonadotropin releasing hormone analogue (sGnRH-a)+dopamine D 2 -receptor antagonist, pimozide (Pim), with parenteral administration. In addition, the effect of co-administration of absorption enhancers and peptidase inhibitors were evaluated. Responsiveness to the treatments was examined using GtH II release. Ten micrograms sGnRH-a and 5 mg/kg of Pim per kg fish bw were used in different formulations and routes of delivery. A mixed micellular intestinal absorption enhancement formulation, consisting of oleic acid and a polyoxyethylenesorbitan (Tween), strongly augmented GtH II release stimulated by sGnRH-a+Pim. GtH II release following treatment did not differ from that obtained after intraperitoneal injection of these drugs. In comparison with the saline control or with intraperitoneal injection, the oral and rectal administration of sGnRH-a+Pim without intestinal absorption enhancement was not effective in stimulating GtH II release. The addition of the enzyme inhibitor, Na 2 EDTA or chicken egg trypsin inhibitor to this formulation was only moderately effective in increasing circulating GtH II levels. Among different Tweens, preformulated with oleic acid in a mixed micellular absorption enhancer for rectal delivery of sGnRH-a at a dose of 20 μg/kg bw in pimozide pretreated carps, Tween 20 and Tween 40, resulted in the highest systemic GtH II levels.

The effects of naltrexone, an opioid receptor antagonist, on plasma LH levels in common carp (Cyprinus carpio L.)

Naltrexone-an opioid receptor antagonist, was administered intraperitoneally to sexually mature male and female common carp in the prespawning period, in order to investigate its effects on spontaneous or sGnRH-A-stimulated LH secretion. Naltrexone and sGnRH-A were injected at the same time. The possible involvement of a dopaminergic system in this process was studied in males pre-treated with pimozide (a dopamine receptor antagonist) 12 h before naltrexone and/or sGnRH-A administration. Blood samples for the analysis of carp LH concentrations were taken just before the injections and then after the injections, serial sampling during 24 h was performed. In male carp, naltrexone (500 or 5000 microg kg(-1)) decreased spontaneous LH release, but there were no effects of naltrexone on sGnRH-A-stimulated LH secretion. In males pre-treated with pimozide, a similar response to naltrexone injection (500 microg kg(-1)) as in pirnozide non-treated fish, was observed. The highest dose of naltrexone, 5000 microg kg(-1), significantly stimulated LH release, in response to sGnRH-A administration in pimozide pre-treated males. In female carp, contrary to males, naltrexone at a dose of 500 microg kg(-1), caused significant stimulation of spontaneous LH release. These data indicate that endogenous opioid peptides modify LH secretion in sexually mature carp. In males, they stimulate LH secretion, acting rather on the hypothalamic GnRH system and in females, opioids inhibit LH release by the influence on the dopaminergic system.

The effect of polychlorinated biphenyls mixture (Aroclor 1254) on the embryonic development and hatching of Prussian carp, Carassius gibelio, and common carp, Cyprinus carpio (Actinopterygii: Cypriniformes: Cyprinidae)

Background. Polychlorinated biphenyls (PCBs) are persistent and bioacumulative chemical pollutants which exert negative physiological effects o n the reproductive system of mature male and female fish. PCBs present in the aquatic environment may also have an influence on developing embryos. The aim of this study was to inves- tigate the effect of Aroclor 1254, a polychlorinated biphenyls mixture, on the embryonic development of Prussian carp, Carassius gibelio (Bloch, 1782), and common carp, Cyprinus carpio L. Materials and methods. The samples of eggs obtained from 4 females of each species were divided into t wo dishes and incubated separately after fertilization (common carp) or activation (Prussian carp) with common carp sperm. The incubation, with Aroclor 1254 (1 or 10 ng · mL -1 ) or in water with no PCB added, lasted for 4 days. The mortality, hatching rate, number of hatched larvae, and number of deformed larvae were observed. Results. After 24 h of incubation of Prussian carp and common carp eggs there were no significant differences in the percentage of living eggs between t he Aroclor 1254 treated groups and the control one. The lowest tested concentration of PCB (1 ng · mL -1 ) accelerated the hatching of Prussian carp larvae at 75 h of incubation. The significant increase in the percentage of deformed larvae was observed only in the experiment with common carp eggs incubated with Aroclor 1254 at the concentration of 10 ng · mL -1 . Conclusion. Results of the presented data showed that Aroclor 1254 (at tested concentrations) is not harmful for the development of activated Prussian carp eggs but teratogenic effect was observed in the case of common carp embryos. K eywords: PCBs mixture, common carp, Prussian carp, embryonic development, reproduction

Differential impact of recombinant human activin on LH secretion in male and female common carp during wintering and spawning period

The pituitaries of male and female common carps were subjected to the treatment with recombinant human activin A. Basal LH secretion decreased in females during wintering, but stimulated basal and sGnRH-induced LH secretion during ovulatory period. It stimulated LH secretion in males during wintering, but not during spawning, suggesting sex-specific effect of activin on LH secretion in common carp.