Locomotion and Behavioral Toxicity in Larval Zebrafish: Background, Methods, and Data - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 146

12.2 BACKGROUND
12.2.1 History
The modern science of behavior can be traced to around the turn of the twentieth
century, when researchers began objectively to study the behavior of animals under
laboratory conditions. Impressions and narratives about behavior were replaced with
numbers, experimental conditions were controlled, and variables were identified and
manipulated leading to repeatable demonstrations of behavior. Automation of
behavioral testing equipment contributed to scientific advances because, in a sense,
it removed the experimenter from the experiment, and prevented any inadvertent
influence on the results due to his or her expectations of the outcome. Automation and
commercialization also increased the breadth of the science by permitting investi-
gation of the same behavioral phenomena in multiple laboratories.
The behavior of any organism is unitary in name only. Several basic processes
comprise the behavioral repertoire of all organisms, and countless studies have shown
the essential conservation of these processes across phyla and species (e.g., Kelleher
andMorse, 1968; Brembs et al., 2002; Greenspan, 2007). There are many schemes for
categorizing behavior. The simplest scheme distinguishes naturally occurring and
acquired behavior. Naturally occurring behavior emerges during development, is
common to a species, and requires no explicit training for its occurrence. Reflexes and
locomotion are good examples of naturally occurring behavior. Acquired behavior, on
the other hand, refers to what is ordinarily called learned behavior because it emerges
with training and experience. Acquired behavior comprises the vast majority of the
repertoire of mammals and several other species, and is considered to result from
cognitive processes originating in the nervous system. Even such a simple scheme is,
however, somewhat misleading because it implies that learned behavior is somehow
not a natural occurrence, when, in fact, all animals learn. It also ignores the fact that
under appropriate conditions reflexes and locomotion can be learned (i.e., modified
through experience).
12.2.2 Development and Toxicity
The commonality of behavioral processes among species is also seen during
development, although the time frames differ widely. Infancy can last for hours to
years, depending on the species. Regardless of the species, the development of
behavior proceeds through well-defined stages involving the emergence of reflexes,
locomotion, sensory competence, neuromuscular coordination and strength, and
learning and memory. The nervous system also proceeds developmentally through
well-defined stages including cellular proliferation, differentiation, migration, syn-
apse formation, and myelination. Proper development of the nervous system and
behavior ensures that an organism is able to adapt to its changing environment, and
consequently grow and survive at least long enough to have the opportunity to
reproduce. The almost clockwork regularities of behavioral and nervous system