Conference of Biological Psychiatry

«Stress and Behavior»

Proceedings of the 9th International Multidisciplinary Conference «Stress and behavior» Saint-Petersburg, Russia, 16-19 May 2005 Editor: Allan V. Kalueff, PhD





O.V. Vyazovska Institute of Biology, Kharkiv National University,

Institute of Children and Adolescents Health Protections NAMS, Kharkiv, Ukraine

It has been proposed that chronic stress noticeably affects behavior in humans and animals. However, mechanisms underlying the changes in behavior after emotional stress are unclear. The aim of this study was to investigate several behavioral measures of stress reaction in the «open field test» in rats. The influence of chronic immobilization stress on a latent period of the first moving, time of staying in the center of the field at the beginning of the test, horizontal and vertical activity, a grooming duration and vegetative index (the number of defecations and urinations) were quantified. This approach allows to estimate behavioral stability of the animal in response to an emotional stress (Mayorov, 1988).

Methods. Male Wistar rats (n = 12), 6 months old were used for this experiment. A semi-automatic device was used to investigate behavioral characteristics of the animals in the «open field test». This device consisted of the rectangular field 140 x 70 cm, divided on the squares (10 x 10 cm), with nontransparent walls, 50 cm height (except the front transparent wall to observe the animals). Sensitive microswitches connected to an area (40 x 30 cm) in the center of the field generated a signal in response to a touch that was registered. The animals were subjected to an immobilization stress during 4 days for 5 hours daily, and tested in the «open field test» on the 5th days. Nonparametric Wilcoxon Mann-Whitney U-test and linear correlation analysis were used.

Results and discussion. Immobilization stress significantly increased the latent period of the first moving from 4.42 ± 2,01 to 8.92 ± 1.59 s (p = 0.045). Time of staying in the center of the field at the beginning of the test increased from 19.68 ± 5.29 to 39.64 ± 5.57 s (p = 0.034). It is believed that latency is an important criterion of emotionality. It had been shown that latency to emerge from a safe compartment into a large, well-lit open field had been decreased by .5 and 1h following stress (Quartermain et al., 1996). These data suggested that acute stress reduces caution by disrupting risk assessment behaviors. Our result indicates that chronic stress, in contrast to acute stress, results in increased caution. Time in the center of the field at the beginning of the test is a complex parameter that includes «freezing» reaction and time required to leave the central area. «Freezing» is considered a marker of strong stress that can be elicited by an exposure of the animal to an unknown environment after chronic immobilization (Walsh, Cummins, 1976). The grooming duration increased from 17.23 ± 3.88 to 50.5 ± 8.73 s (p = 0.0025), in agreement with previous reports in models of «anticipation» stress (Mayorov, 1988), and repeated restraint (D’Aquila et al., 2000). The vegetative index did not change significantly. A positive correlation between time of horizontal and vertical activity, (r = 0.89: p = 0.0001) constitutes an evidence for coordinated neuronal mechanisms of these types of reactions, which seem to be related to orientation, exploration and agonistic activity. Similar result was reported earlier in an experiment with model of «anticipation stress».

ISSN 1606—8i8i

Exploratory behavior is probably related to an avoidance reaction (Mayorov, 1988). Overall, our data demonstrate that chronic immobilization results in increased caution and fear that is indicated by increasing of latency time of the first moving, time in the center of the field at the beginning of the test, and re-directed activity such as grooming. Significant correlation between the horizontal and vertical activity reflects exploration and avoidance reactions observed.

ISSN i606—8i8i