Academic journal article The Spanish Journal of Psychology

Self-Starvation in the Rat: Running versus Eating

Academic journal article The Spanish Journal of Psychology

Self-Starvation in the Rat: Running versus Eating

Article excerpt

Rats given the combination of unrestricted access to an activity wheel and restricted access to food can lose weight to the extent that they will die unless removed from these conditions. Although this has been known for forty years, why this happens has remained unclear. The phenomenon is paradoxical in that one might expect such rats to eat more as their weight decreases, but in fact they eat less than resting controls. This lecture first examines some of the factors than influence whether self-starvation will occur, such as age, time of food access, type of food and ambient temperature. It then compares competing explanations such as circadian adaptation, thermo-regulation and food aversion learning. As so often in psychology, it turns out that selfstarvation results from a combination of many separate factors. The general implications of this research are examined, including whether it provides a useful animal model for human anorexia nervosa.

Keywords: self-starvation, rats, anorexia nervosa

Las ratas sometidas simultáneamente a restricción de comida y acceso a una rueda de actividad pierden peso hasta el extremo de morir si no son retiradas a tiempo de estas condiciones. Aunque este hecho es conocido desde hace cuarenta años, la razón por la cual esto sucede permanece sin resolver. Lo paradójico de este fenómeno reside en que, aunque sería esperable que las ratas comiesen más a medida que su peso disminuye, en realidad estos animales comen menos que sus controles sedentarios. En esta conferencia se examina, en primer lugar, algunos factores que influyen en el desarrollo de la auto-inanición como son la edad, el tiempo de acceso a la comida, el tipo de comida y la temperatura ambiental. A continuación se comparan algunas explicaciones tales como la adaptación del ritmo circadiano, la termorregulación y la aversión adquirida a la comida. Tal como ocurre con frecuencia en psicología, la auto-inanición es el resultado de diferentes factores. Finalmente, se examinarán algunas implicaciones más generales de esta investigación, incluida su posible utilidad como modelo animal para el estudio de la anorexia nerviosa en humanos.

Palabras clave: auto-inanición, ratas, anorexia nerviosa

Historical Background

Richter is sometimes known as the "father of the biological clock" for his pioneering research on biological rhythms that started in the 1920s and continued for some decades (Richter, 1922; Schulkin, 2005). Much of this research used a simple piece of equipment, the activity wheel, which has remained essentially unchanged ever since. The standard (Wahmann) type consists of a round drum made of a metal frame and mesh, with a diameter of about 330 mm so that each complete revolution made by a rat walking or running inside corresponds to a distance of about 1.1 m. Attached to the wheel is a side cage with a door that leads to the wheel. Under open wheel conditions, an animal can move freely between wheel and cage, whereas under closed wheel conditions, an animal is confined to the wheel by shutting the door.

A basic finding made by Richter (1922) was that for rats living in an open wheel condition, when and how much they run is subject to a diurnal rhythm: The nocturnal rat runs a great deal at night, but little during daylight hours. What was discovered much later is that running can also become subject to an independent biological clock set by when food is made available. If access to food is restricted to a few hours at a regular time each day, a rat will come to run increasingly during the preceding 3-4 hr period (food anticipatory period; FAP) even if this is during the daytime (e.g., Mistlberger, 1994).

Another factor that determines how much a rat will run is weight loss: A rat with restricted access to food runs much more than one with unrestricted access. The relationship between weight loss and activity was very important for Hull's concept of general drive that was central to his theory of motivation (Hull, 1943). …

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