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SummaryLevels of endogenous or administered substances can be estimated by blood sampling. This allows an evaluation of the relationship between clinical signs, physiological parameters, pharmacological treatments and behaviour of the animal. We show that blood samples can be taken occasionally as well as sequentially by means of a small incision at the end of the rats' tails. Up to 300 III of blood can be collected within 90 s. The advantages of this method are: (i) anaesthesia and surgery or restraint of the animal are not necessarYj [iiI the procedure can be considered stress-free as indicated by the low, basal levels of the stress hormone corticosterone, even with frequent sequential blood sampling over 3 hj and (iii) it can be used for longitudinal studies allowing intra-individual comparisons over months and even years. Blood samples collected via an intravenous catheter and, at the same time, by our tail incision method resulted in comparable amounts of corticosterone. Moreover, we consider the tail incision method for rats to be 'animal-friendly' and a real alternative to other conventionally used blood sampling techniques.

As there is little known about age-related changes in the hypothalamic-pituitary-adrenal (HPA) axis of mice, we determined the daily patterns of corticosterone secretion every 2 h, together with adrenocorticotropic hormone (ACTH) release and central HPA axis markers in the morning and evening of 3-, 9- and 16-month-old male C57BL/6J mice. We observed that: (i) corticosterone secretion showed a distinct age-related circadian pattern. During the light period this was expressed by relative hypercorticism in 9-month-old mice and relative hypocorticism in 16-month-old mice. ACTH was elevated at 16 months of age; (ii) mineralocorticoid (MR) and glucocorticoid receptor (GR) mRNA expression in the hippocampus was significantly decreased in 9-month-old mice, whereas in 16-month-old mice, expression was similar to young animals. Circadian variation was modest in all age groups; (iii) the parvocellular hypothalamic paraventricular nucleus (PVN) expressed very high vasopressin mRNA, which was subject to circadian variation in 3- and 9-month-old mice. Furthermore, significant levels of MR mRNA were expressed in the PVN. In conclusion, basal HPA axis activity and expression of its central regulatory markers are age-dependent in mice. This suggests that the capacity to adjust to environmental demands is either a function of age, or depends on different dynamics of the HPA axis.

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Spatialleaming and memory in rodents is most often assessed in the Morris water maze. Neurobiologists have to distinguish behavioral patterns to unravel underlying neuronal systems. Weanalyzed swimpatterns of mice videotaped before and after training with a multitrial procedure in the water maze. In addition to traditional parameters, the animals' position in relation to trained and other possible platform locations was estimated five times per second by an image analysis system. This parameter, cumulative distance to platform, was correlated with time spent in the platform quadrant but not with latency to and crossings of the platform location. We detected a subgroup of animals with concentric patterns within the group of spatial/persistent patterns. Random patterns were classified as well. Swim patterns before training were not predictive for the one after training. In summary, image analysis systems have made it very convenient to quantify behavior. Usingtheir capacity, we have further improved the analysis of swim patterns, revealing animals' different approaches to solve a problem.Behavioral biologists are confronted with the problem of how learning and memory can reliably be quantified using behavioral measures. Automated video-tracking and image analysis systems have made it very convenient to quantify the performance of animals in behavioral tasks and have made it possible to calculate many parameters. One of the most frequently used tasks to measure spatial learning and memory ofrodents is the Morris water maze (Morris, 1984). Various procedures (e.g., multitrial, reversal, delayed matching to place) have been developed to examine the neurobiological basis oflearning and memory (Brandeis, Brandys, & Yehuda, 1989; Poucet & Benhamou, 1997). Since the creation of mutant mice, the multi trial procedure in the water maze has become the standard and most widely used behavioral task (Wolfer, Stagljar-Bozicevic, Errington, & Lipp, 1998). Specifically, the analysis and interpretation of this multi trial water maze procedure requires refinement.Briefly, in a pool of warm water, animals are trained to locate a platform in a fixed position just below the water surface. During several days, a number of trials are given (i.e., multitrial procedure). The animal's ability to find it most efficiently depends on the use ofa configuration of cues surrounding the pool. Allowing the animal to swim for a fixed time without the platform (i.e., free swim, probe, or transfer trial) reveals the search strategy. Learning is defined by shorter latencies and by decreased path length to the platform. Because the path to the platform is in no way constrained, different strategies are possible, each of which may result in successively shorter escape latencies. For example, animals that direct their search predominantly to the area ofthe maze where the platform was located during training can have the same latency to the platform as animals that use a circular strategy, but do not show direct search toward the platform area (Schenk & M...