E. V. Koplik – Ph.D. (Med.), Associate Professor, Leading Research Scientist, P.K. Anokhin Institute of Normal Physiology (Moscow). E-mail: firstname.lastname@example.org
In the study presented, the hypothesis was tested that behaviour of rats under the open field test condition and effects of subsequent acute stress relate to conformational properties of the main plasma carrier protein, albumin.
To evaluate albumin properties, fluorescence intensity of a molecular probe CAPIDAN (N-carboxyphenylimide of dimethylaminonaphthalic acid) at N (at pH 7.4) and F (pH 4.2) albumin conformation was measured and the N–F signal ratio was calculated. 
Behaviour of 78 Wistar male rats was characterized from the fraction of time taken for exploratory and ambulatory activity during the open field test . In rats not subjected to stress (n = 40), a negative correlation was revealed between open field test activity and CAPIDAN N-to-F ratio for albumin (r = 0.55, p < 0.0005). In the group of rats subjected to acute stress (immobilization plus stochastic electrostimulation) the correlation between behavioural activity and the albumin conformational properties was significantly positive (r = 0.59, p < 0.0001): the CAPIDAN albumin fluorescence ratio increased in the highly active rats and decreased in the low-activity rats. The mechanisms of the observed effects may involve differences in nonesterified fatty acid production during stress.
Differences in albumin conformational state found in rats with different behaviour proved to be significant in experimental hemorrhage stroke. That was shown in the series of experiments on 84 Wistar male rats. In this series 24-hour immobilization was used as stress loading. To characterize albumin state, the method of CAPIDAN fluorescence quenching with nitrate was used additionally to mentioned above. This method makes it possible to evaluate steric accessibility of albumin binding sites.
In rats with low behavioural activity the accessibility of albumin binding sites was significantly (p < 0.05) lower than in active rats. Nevertheless, the tendency to normalization of this parameter was observed during 3–7-th days of the disease. In rats loaded to stress before hemorrhage the opposite tendency was observed: the accessibility decreased in the stroke course and this decrease was more dramatic in low-activity rats.
Thus, the rats with different behavioural activity in the open field test are different in conformational state of albumin binding sites. This differences correlate with the peculiarities of the course of experimental hemorrhage. Previous stress loading leads to the increase of the severity of the disease to dramatic damage of albumin binding sites.