376 0090-2977/14/4604-0376 © 2014 Springer Science+Business Media New York Neurophysiology, Vol. 46, No. 4, August, 2014 Do Results of the Open Field Test Depend on the Arena Shape? S. V. Grabovskaya 1 and Yu. T. Salyha 1 Received May 05, 2014 The open field test (OFT) is one of the main methods used for the estimation of behavioral indices and emotionality levels in animals. This test is widely used in toxicological and pharmacological studies. The question of whether the arena shape influences the results of testing remained open. This is why we compared the results of the mentioned test using one and the same species of laboratory animals (rats), identical conditions of testing, and arenas of nearly the same area but of a round or square shape. Significant differences were found in only two examined parameters, frequency of realization of the burrow reflex and intensity of “internal” horizontal motor activity; other indices showed nearly no considerable differences. Thus, it can be concluded that the results of behavioral studies carried out under the above two conditions are rather similar to each other in their adequacy. Keywords: open field test, behavioral indices, arena shape, rats. Institute of Biology of Animals of the National Academy of Sciences of Ukraine, L’viv, Ukraine Correspondence should be addressed to Yu. T. Salyha (yursalyha@yahoo.com) INTRODUCTION The open field test (OFT) is one of the most popular and extensively known methods in the investigation of animal behavior. It was introduced into the scientific practice in 1932 by Hall [1]. This test is based on the natural drive of animals, rodents in particular, to examine a novel territory; the respective behavioral phenomena are dissimilar in animals with different levels of emotionality [2]. Most frequently, the OFT is used in investigations of behavioral phenomena in mice [3, 4] or rats; there are also studies carried out on gerbils [5], vole mice [6], hamsters [7], dogs, primates, fish [8], and even humans (10-month-old or younger children) [9]. In the course of testing, the animals are placed in a square or round arena open on top and limited by walls from the sides. Rectangular arenas with different ratios of the side lengths are used considerably more rarely. Materials for arenas used in different studies vary (plastics, wood, metal, rubber, or even glass); colors of the walls also can be different (from white to black) [9]. The floor of the arena is divided into squares (in the case of square or rectangular arenas) or into segments (in round arenas). As a rule, the internal space of the arena is empty; some authors, however, place in this space some additional objects (e.g., mirrors, pieces of food, flashing sources of light, other animals in cages, etc.). The testing period for one animal is usually 3 to 5 min long; this period, however, can be prolonged to one hour [10] or even longer. Observation of the animal’s behavior is carried out; indices of the latter are recorded immediately in the course of the testing period, or behavior is videorecorded for off-line analysis. The main examined parameters are the following: (i) horizontal motor activity (number of the squares or segments crossed by the animal within the observation period), this index most closely resembles the intensity of locomotion; (ii) vertical motor activity (number of the vertical risings on the hindlimbs); (iii) number of defecations; (iv) number of urinations, and (v) number of grooming episodes. In addition, hori- zontal motor activity is frequently divided into external (crossing the squares or segments near the wall of the arena) and internal (movement of the animal toward the central part of the arena and crossing the central squares of segments). Grooming can be classified as short-lasting (two of three movements of the forelimbs near the head) or long- lasting (more movements combined with cleaning of other parts of the body). The so-called burrow reflex is interpreted as one of the indices of research activity; this is sniffing of burrow-like openings in the floor and attempts to enter them in the case of sufficient dimensions. Some authors divide vertical motor activity into a free one (risings on the hindlimbs with no support) and that manifested near the wall (with a support) [1]. There are studies where some