Assessment of Motor Function in Rodents: Behavioral Models Sharing Simplicity and Multifaceted Applicability

Abstract

The open-field test was originally described by Hall (1934) for the study of emotionality in rats. As reviewed by Prut and Belzung (2003), the procedure consists of subjecting an animal, usually a rodent, to an environment from which escape is prevented by surrounding walls. Hall’s apparatus consisted of a brightly illuminated circular arena of about 1.2 m diameter closed by a wall of 0.45 m high. Hall used defecation and urination in the above-described open-field to measure individual differences in rats’ emotionality. Thenceforth, the use of this test has diversified enormously, differing, for example, in shape of the environment (circular, square, or rectangular), lighting, subjects, and mainly in the behavioral parameters quantified (see Walsh and Cummins 1976; Belzung 1999; Prut and Belzung 2003 for review). This concern notwithstanding, during the last 70 years, the open-field test has become one of the most (likely the most) widely used test in neuropsychobiology and neuropsychopharmacology. Indeed, even nowadays, studies using this very simple method have been published in the best periodicals of biological psychiatry (Abílio et al. 1999, for example), neurobiology of aging (Silva et al. 1996, for example), and neuropsychopharmacology (Chinen et al. 2006, for example).

The whole is more than the sum of its parts. The profound complexity of biological beings cannot be reproduced in either the test tube or culture dish. Neuroscience research, in particular, critically depends on behavioral experimentation. However, while ethical and technical issues preclude the use of human subjects for many important experiments, a number of factors also limit the widespread use of non-human primates (see Jinnah et al. 2005). Thus, the majority of research on behavioral animal models has focused on other species, particularly small rodents such as rats or mice.

Within this context, the evaluation of rodents’ motor activity is crucial for the correct interpretation of behavioral models of memory, anxiety, depression, aggression, addiction, etc. Conversely, emotionality, memory, and other “mental states” can dramatically modify specific animal models of movement disorders. Indeed, the intricate circular connection between mental states and motor function is splendidly defined by Walle Nauta’s question: “What is a thought except a movement that is not connected to a motor neuron?”

Assessment of motor activity and movement disorders in rodents may, therefore, lead to an unlimited source of scientific knowledge. The aim of the following chapters is not to exhaustedly describe and discuss either the multiple methods available for assessing rodents’ general activity (see Pierce and Kalivas 1997 for this purpose) or rodents’ models of specific movement disorders (see Jinnah et al. 2005). These three chapters will critically discuss three rodent models of motor function that share two marked characteristics: simplicity and wide applicability. All of the to-be-discussed models (open-field, catalepsy, and orofacial dyskinesia) are simple to perform and each respective apparatus can be bought by or constructed in any laboratory in the world. From another point of view, while the first two models (open-field test—Chap. 26 and catalepsy test—Chap. 27) can be used to investigate several neuroscientific parameters beyond motor function, the last model to be discussed (orofacial dyskinesia—Chap. 28) evaluates a movement disorder shared by many different neurological diseases. These are ideal models for researchers who believe that science is built from ideas, not just money and technology.

This chapter is dedicated to Dr. João Palermo-Neto, who initiated Dr. Frussa-Filho and many other Brazilian neuroscientists into the exciting world of the open-field model.