The abuse of anabolic androgenic steroids (AAS) is becoming increasingly common and may result in a range of physiological as well as psychological effects such as altered behavior in terms of increased aggression, cognitive dysfunction and addictive behavior. AAS comprise testosterone and its derivatives, of which nandrolone is one of the more common. Previous studies have shown nandrolone-induced effects in male rats on peptide levels within the Substance P (SP) system and the dynorphinergic system; these effects may be linked to some of the reported behavior alterations. The studies presented in this thesis aimed to investigate the mechanisms underlying these peptide alterations and also to further investigate neuropeptidergic effects attributed to nandrolone administration. The results display significant effects on the enzymatic conversion of SP and Dynorphin A into their bioactive metabolites SP(1-7) and Leu-enkephalin-Arg6, respectively, as a result of nandrolone treatment. More profound investigations on the dynorphinergic system displayed effects on the kappa opioid receptor density in various brain regions. There was also a significant increase in the expression of the gene transcript of prodynorphin in the hippocampus, a brain region associated with cognitive processes. In addition, impaired spatial learning and memory in the Morris water maze task following nandrolone administration was encountered. The results provide further understanding regarding neuropeptidergic mechanisms underlying AAS-induced behavioral effects.

Background Animal models can be used to mimic human conditions of psychopathology, and also as pre-clinical models to evaluate candidate drugs. With hormonal treatment it is possible to produce behavior in the rat which corresponds to the mental symptoms of pre-menstrual syndrome (PMS), and pre-menstrual dysphoric disorder (PMDD). PMS affects 25-30 % of all women in fertile age and 3-8% are diagnosed with the more severe condition PMDD. The cardinal mental symptoms are; irritability, mood-swings, depression, anxiety, fatigue, insomnia, difficulties with concentration and memory and learning difficulties. The symptoms of PMS/PMDD occur in the luteal phase in conjunction with increasing concentrations of progesterone (P4) and P4-metabolites. In anovulatory cycles the symptoms are absent. The hormones which produce the monthly reoccurring negative symptoms on mood are foremost the neuroactive metabolites; allopregnanolone (ALLO) and tetrahydro-deoxycorticosterone (THDOC). ALLO is produced by the corpus luteum, but can also be synthesized in the brain, both ALLO and THDOC can also be released from the adrenal cortex during stress. These steroids are active on the inhibitory GABA neurotransmitter system through the GABAA receptor, and the effects are similar to that of alcohol and benzodiazepines. These steroids have strong sedative and hypnotic effects. A paradox is that some individuals seem to react with negative mood on sex steroids while all fertile women have the cyclical steroid changes during the menstrual cycle. Some individuals are more sensitive to neuroactive steroids with influences of personality, heritability and stress factors. Aims The thesis aims were to develop pre-clinical animal models of PMS/PMDD and to investigate induction of ALLO tolerance, individual sensitivity to neurosteroids and the interactions between chronic social stress and neurosteroids. Methods In these studies male and female Wistar rats were used to test steroid hormone effects on learning and memory and behaviors analogous to negative mood symptoms. This was accomplished through hormonal treatment and a subsequent withdrawal period from P4 (P4) + estradiol (E2) (PEWD), or ALLO. To assess tolerance, memory and learning in the Morris water maze (MWM) was studied. Anxiety-like behaviors were tested with the elevated plus maze (EPM), open field test (OFT), and the intruder test (IT). The EPM or OFT was used to classify the rats as high or low responders on risk-taking and explorative behavior (HR/LR). For social ranking order assessment the tube test (TT) and food competition test (FCT) were used. Chronic social stress was accomplished through co-habituation with two older rats (chronic subordination stress). In female rats the estrous cycle followed using staining of vaginal smears. Concentration of corticosterone (CORT) was measured by radio-immuno-assay (RIA). Results In the MWM ALLO pre-treatment produced tolerance to the acute negative ALLO effects. Both male and female rats showed behavioral correlations between the EPM and OFT tests, and correlations were also seen in CORT levels. Individuals with the stable trait of high risk-taking and explorative behavior (HR) were more sensitive to PEWD induction of anxiety-like behavior. These animals also showed decreased CORT levels during withdrawal. Chronic subordination stress enhanced the response to PEWD on measures of locomotor activity and social anxiety-like behavior. Conclusions It is possible to induce tolerance to the negative ALLO effects on learning and memory. The animal models of anxiety-like behavior show an individual PEWD response profile where HR rats are more sensitive. Exposure to chronic social stress enhanced the PEWD response. Hence there are both inherent and environmental factors behind the behavioral response to steroid hormones in rats. / Stress- och könshormoners verkningar på centrala nervsystemet