Some properties of the time-course stabilization of running behavior of rats living in activity wheel units.

Abstract

It is important to have information about the duration of the adaptation period required for stable running rates in activity wheels both for planning the length of experiments and for scheduling treatments following the adaptation period. Much activity research circumvents problems of apparatus differences by using each animal as its own control, allowing treatment effects to be expressed as a percentage of the activity during the adaptation period (e.g., Finger, 1951). But such percentages are influenced by the extent to which activity stabilized during adaptation. If it were still increasing, for example, treatment effects would be confounded with the irscrease. Even if mean group running rates showed no significant slope across days, unstable individual rates could impair the sensitivity of an experiment by contributing variability. Discussions of the length of adequate adaptation periods leave the impression that 10 to 21 days suff~ce. Munn (1950, p. 77), citing Shirley (1928b), wrote She claimed that at least ten days of adaptation to the cages are essential. Hall (1961, p. 116; cites another article by Shirley (1928a) to the effect that young rats just nine days to become adapted to the activity wheel and older animals (100 days of age) require 15 Hall also discusses the work of Eayrs (1954) showing that 21 days may be required but points out that Eayrs used females, whose estrus cycle may have made the lengthy adaptation period necessary. In the course of several experiments it became dear that, while individual running races did stabilize, time periods in excess of the above were required. SS were 23 male albino rats born of pregnant females supplied by the Holtzman Co. All Ss were reared from birth in a 12-hr. light/dark cycle until age 60 days, when they were put in enclosed Wahmann LC-34 activity wheel units which have a small living cage acached to an activity wheel. All wheels were equated for frictional torque (Lacey, 1944) and modified as suggested by Lockard ( 1965 ) . The same light/dark cycle and other laboratory conditions dining rearing continued. Each S lived in a unit for 135 days. The first 80 were an adaptation period with constant conditions of ad lib. food, water, and wheel. On Day 81 Ss were shut off from the wheel by a sliding door for 2 to 6 days, after which the door was open for the remainder of the experiment. The adaptation conditions then continued through Day 129, after which 6 days of either food or