The seasonal reproduction of the three-spined stickleback is stimulated by long day photoperiod. As in other vertebrates, the reproductive system of stickleback is regulated by the brain-pituitary-gonadal (BPG) axis which is largely controlled by feedback effects. Both negative and positive feedback effects on the BPG axis have been found in fish. So far, the roles feedback effects on the BPG axis play in the photoperiodic regulation of seasonal reproduction are still unclear. This thesis focused on the photoperiodic regulation and gonadal feedback effects on the gene expressions of gonadotropin (GtH) and gonadotropin-releasing hormones (GnRH) in the brain and pituitary, and how gonadal feedback regulated the steroid homeostasis in stickleback.Both GnRH2 and GnRH3 mRNA was found in the hypothalamus. Higher expression levels of both GnRH2 and 3 in breeding than in post-breeding males suggested that they are both involved in seasonal reproduction. There was no evidence for a role of GnRH3, which may be the dominating form, in the photoperiodic control of reproduction. However, the polarity of the feedback effect on gnrh3 gene expression may turn from positive to be negative when the males went into post-breeding state. Tapeworm, Schistocephalus solidus, infection inhibited the reproduction of sticklebacks. However, the infection caused higher expression levels of both GnRHs and GtHs genes, which may be due to feedback effect on the BPG axis.Under short day, both lh-β and fsh-β were suppressed by low androgen levels. This negative feedback may inhibit maturation completely, unless a rise of androgens triggers positive feedback under long day. The change in feedback polarity may result in all or nothing maturation. Furthermore, the androgen inhibitory effect on lh-β and fsh-β under short day could be abolished by aromatase inhibitor, which means the estrogen may cause negative feedback in males under short day.There was no compensation effect on plasma androgen level in fully mature hemi-castrated fish. However, both testosterone and 11-ketoandrostenedione treatments increased plasma levels much less in sham-operated fish than in castrated ones, indicating that homeostatic mechanisms are nevertheless present. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows<strong>:  </strong>Paper 1: Submitted. Paper 3: Submitted. Paper 4: Submitted.</p>

Background. There are a number of studies showing that general practice is one of the most stressful workplaces for health care workers. Since the Baltic States regained independence in 1990, a reform of the health care systems took place in which a new role and more responsibilities were allocated to general practitioners. This study aimed to explore the psychosocial stress level among Lithuanian general practitioners (GPs) and examine the relationship between their psychosocial stress and work characteristics. Methods. A cross-sectional study was made of 300 Lithuanian general practitioners. Psychosocial stress was investigated with a questionnaire based on the Reeder scale. Job demands were investigated with the Karasek scale. The analyses included descriptive statistics, interrelationship analysis between the different characteristics, and multivariate logistic regression to estimate odd ratios for each of the independent variables in the model. Results. The study shows that 48% of the respondents could be classified as suffering from work related psychosocial stress by the Reeder scale. The highest job strain prevalence was among widowed, single and female GPs. The lowest job strain prevalence was among males and GPs of older age. Job strain occurs when job demands are high and job decision latitude is low. Conclusions. The greatest risk to physical and mental health from stress occurs to general practitioners facing high psychological workload demands combined with... [to full text]

Marked shifts in the life history traits of fish have been reported in many exploited fish stocks, with a particular trend towards decreasing size and age at maturity. Though other environmental and behavioural factors have been implicated, the key driver of these changes links to fishing pressure, through both the direct selective effects of fishing itself, and indirectly through the manipulation of important biological and environmental factors. Although reproduction itself has been well described in teleosts, the mechanisms of environmental and endogenous entrainment of maturation remain unclear and it was the principal aim of this thesis to improve current understanding of these systems in gadoids. Photoperiod has been identified as the strongest environmental cue for entraining seasonal behaviours, including seasonal reproduction. Over the last decade, several of the key drivers involved in the photoneuroendocrine cascade have been elucidated in mammals and birds, with the Eya3 pathway merging as an important mechanism for entraining maturation. However, little is yet known of their influence on maturation in fish. In the first study, the photoperiodic regulation of the Eya3-Tshβ-Dio2 cascade was analysed in Atlantic cod exposed to either continuous light (reproductive inhibition) or simulated natural photoperiod (reproductive stimulation) from July to December. Monthly expression was measured through QPCR, demonstrating a strong activation of pituitary Eya3 under declining photoperiod. As this coincided with the onset of secondary gametogenesis, these results suggest that Eya3 may play a stimulatory role in the photoneuroendocrine cascade of Atlantic cod. Although photoperiod represents the most reliable and noise free proximate signal to entrain the reproductive process, it is clear that a minimum growth and energetic state must be reached for maturation to progress. This directed the second line of study – a series of diet restriction trials on haddock and cod designed to investigate the influence of naturally occurring lipid levels in the diet on growth and reproduction, define the “critical window” in which fish assess their energetic state and how this is analysed before commencing secondary gametogenesis, and to assess whether Eya3 is regulated by the growth axis in cod. The results of these experiments indicate that overall size around the autumn equinox is the most accurate indicator of maturation commitment in cod. Additionally, Eya3 expression was elevated in maturing fish indicating a role for this marker in linking the energetic signal with entrainment of the reproductive axis. Finally, an analysis of the physiological and genetic stock structure of cod from the North Sea IVa stock region and westward into VIa was performed. The results of this analysis support previous genetic studies, indicating further fine-scale structuring of these stocks, reflective of the structure indicate by the differences in maturation strategies of the component populations. The results identified both environmental and harvest related pressures which may be driving the current stock structure. The results of these studies greatly improves our understanding of the key drivers and mechanisms regulating maturation in cod, highlighting new avenues for future research.

Reproduction in vertebrates, including fishes, is under control of the brain-pituitary-gonad (BPG) axis. The female three-spined stickleback, Gasterosteus aculeatus, produces egg clutches at intervals of a few days and spawns them in a nest built by male. Following ovulation, eggs are stored in the ovarian cavity surrounded by the ovarian fluid (OF). If spawning or spontaneous release do not occur, the eggs can undergo overripening, a phenomenon occurring both in nature and captivity. In this PhD thesis, the changes of reproductive hormones and vitellogenesis were studied at overripening of eggs and over the natural spawning cycle. OF properties were also examined at overripening of eggs and after treatment with sex steroids. Plasma levels of steroids: testosterone (T), estradiol (E2), 17,20β-dihydroxypregn-4-en-3-one (17,20β-P) and 17,20β,21-trihydroxypregn-4-en-3-one (17,20β,21-P) were measured by radioimmunoassay, and relative mRNA levels of the pituitary gonadotropins (fsh-β/lh-β), brain gonadotropin-releasing hormones (gnrh2/gnrh3) and kisspeptin and its receptor (kiss2/gpr54) by qPCR. Overripening of eggs was accompanied with a significant reduction in most of endocrine parameters of BPG axis (T, E2, 17,20β-P; lh-β; kiss2, gpr54). Low level of hormones could be advantageous for the overripe egg-bound females, since this would reduce further ovulations giving higher chances to survive and reproduce again. Over the 3-day spawning cycle, T and E2 were highly correlated, showed cyclicity with low levels at ovulation and increasing from 24 and 6 hours post-spawning (hps), respectively. Spawning may give rise to this increase as these rises did not occur if release of the eggs does not happen (overripe females). A peak at pituitary lh-β mRNA levels appeared 48 hps, a day before the next ovulation. No significant changes were found for the other studied hormones. Vitellogenesis was studied by measurement of the vitellogenin mRNA levels in the liver by qPCR. The levels were highest at 24 and 48 hps and were positively correlated to both E2 and T over the cycle. However, changes were small suggesting a rather continuous vitellogenesis over the stickleback spawning cycle which could be an advantage for a multiple spawner with a limited spawning season. Overripening reduced vitellogenin mRNA levels but did not abolish it. OF amount was diminished in overripe females and had a lower viscocity but higher dry weight and protein levels than in non-overripe ovulated females, suggesting that changes in OF properties are related to the egg overripening. The effects of steroids were studied using Silastic capsules. T and 17,20β-P induced an increase of OF amount, but protein levels were only increased in 17,20β-P-treated females, proposing a role of this steroid in the control of OF secretion. 1-D SDS-PAGE showed that OF contained several proteins, some of them came from eggs, but no consistent differences between groups. Concluding, the knowledge of the reproductive physiological changes is important for understanding their essential roles in the production of viable eggs in this species but also in the reproductive physiology of female fishes in general. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.</p>