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There is no abstract available for this dissertation.

Secretoneurin (SN) is a 31-43 amino acid, functional peptide derived by proteolytic processing from the middle domain of the ~600 amino acid secretogranin-II (SgII) precursor. In teleosts there are 2 forms arising from 2 different genes, SgIIa and SgIIb. In turn, there are both SNa and SNb in teleost. Secretoneurin is a well-conserved peptide during evolution from fish to mammals and widely distributed in secretory granules of endocrine cells and neurons. Secretoneurin plays important roles in different biological processes, for example controlling vertebrate reproduction by stimulating luteinizing hormone release from the pituitary. A potential new role of SN in feeding in goldfish is the subject of the research presented in this thesis. Firstly, we looked at the distribution of SgIIa mRNA in various female goldfish tissues using both RT-PCR and Q-PCR techniques in order to determine which tissue expresses SgIIa mRNA and in which level. We found that SgIIa mRNA was detected in different amounts in all tissues examined. The main tissues of interest were hypothalamus, telencephalon and gut, they all expressed SgIIa. Secondly, we examined the effect of acute (26 h), short (3 days), medium (7 days) and long (14 days) fasting and periprandial changes on SgIIa mRNA level in hypothalamus, telencephalon and gut using Q-PCR method. The results showed that SgIIa mRNA increases under the effect of acute and short fasting, however, medium and long fasting did not affect SgIIa mRNA. Thirdly, we examined the effect of brain injection of goldfish SNa on food intake and locomotor behavior and the expression of some feeding neuropeptides such as neuropeptide Y, orexin, chocystokinin and cocaine-and amphetamine-regulated transcript I after treatment. Injection of SNa in the third brain ventricle increased food intake and fish activity. Associated with this was an increase in NPY and decrease in CARTI mRNA levels in hypothalamus. The increase in SgIIa mRNA following fasting and the increase of food intake as a result of SNa treatment suggest a novel role for SNa in feeding processes.

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In Experiment 1, groups of 10 goldfish and of 10 grey mullet were trained to press a lever for food under a fixed, daily, light cycle. The periods during which responses were reinforced were restricted to two, 1-hr periods in every 24 hrs. These periods occurred at the same time each day. Responses were coordinated with the temporal contingencies of the schedule, and this pattern persisted for a number of days when no responses were reinforced. Experiment 2 demonstrated that a fixed light cycle was not essential for the maintenance of temporal discrimination. Experiment 3 followed a similar procedure to that of Experiment 1, except with individual goldfish and with only one, 1-hr feeding period in every 24. Experiment 4 produced evidence that temporal discrimination could develop under continuous illumination in individual goldfish. In Experiment 5, individual goldfish under continuous illumination were exposed to schedules that reinforced lever presses with food during a 1-hr period each day. Training with simultaneous temporal and visual contingencies, where food was available only in the presence of a stimulus light and at the same time each day, did not attenuate control over responding by either contingency. Further, pretraining on the temporal contingency did not prevent the subsequent acquisition of control by a stimulus light that was presented during the feeding hour. Similarly, pretraining on a visual contingency in which food was available at a different time each day did not prevent the subsequent acquisition of control by the temporal contingency (established by fixing the time of food availability). In Experiment 6, pretraining on the visual contingency did attenuate the subsequent acquisition of control by a different visual stimulus, showing that the lack of interference in control observed in Experiment 5 was not simply due to the intertrial interval used. These findings suggest that concurrent temporal and visual contingencies may control behaviour in parallel rather than in a competitive manner.