Serotonin (5-HT) plays an important role in depression and specific 5-HT reuptake blockers appear to be clinically important antidepressants. It is unclear however, which serotonergic mechanism is involved in the antidepressant effect, certainly when regarding the existence of at least seven 5-HT receptor subtypes. By testing different 5-HT ligands in two animal models of depression (forced swimming and DRL72-S test) and comparison with data from literature, evidence is provided for potential antidepressant qualities of 5-HT1A receptor-agonists and 5-HT1C receptor-antagonists. Compounds binding to 5-HT1B, 5-HT2 and 5-HT3 receptors do not have an antidepressant profile. Results of clinical research support the predicted antidepressive effects of 5-HT1A receptor-agonists.

The impact of body density (BD) on an animal's capacity to sustain a workload is important in the accuracy of evaluating swimming exercise in rats and the associated training protocols. The aim of this study was to quantify the influence of BD the maximal lactate steady-state (MLSS) workload in swimming rats. The BD of ten 90-day-old rats and sixteen 120-day-old rats was determined by underwater weighing, and their aerobic capacity was determined by the MLSS test. The MLSS blood concentration values were 4.11 ± 0.96 mmol l− 1 in the 90-day-old rats and 4.81 ± 1.49 mmol l− 1 in the 120-day-old rats. There was no significant (P>0.05) difference between these values. The older rats were more dense (P < 0.001) and showed a significantly increased (P < 0.001) absolute effort and relative-to-body-weight effort to keep themselves on the water surface when compared with the younger rats. BD can significantly affect an animal's capacity to sustain work within this age range, and individual fluctuation in effort should be determined to avoid mistakes when interpreting the results. This is particularly important in longitudinal studies in which the intervention or ageing process can modify the animal's body composition. Our results quantify the effects of BD on the performance of rats in the MLSS test.