A gravimetric method for the measurement of total spontaneous activity in rats

Currently available methods for the measurement of spontaneous activity of laboratory animals require expensive, specialized equipment and may not be suitable for use in low light conditions with nocturnal species, We develop ed a gravimetric method that uses common laboratory equipment to quantify t he total spontaneous activity of rats and is suitable for use in the dark, The rat in its home cage is placed on a top loading electronic balance inte rfaced to a computer, Movements are recorded by the balance as changes in w eight and transmitted to the computer at 10 Hz. Data are analyzed on-line t o derive the absolute value of the difference in weight between consecutive samples, and the one-second average of the absolute values is calculated. The averages are written to file for off-line analysis and summed over the desired observation period to provide a measure of total spontaneous activi ty. The results of in vitro experiments demonstrated that: 1) recorded weig ht changes were not influenced by position of the weight on the bottom of t he cage, 2) Values recorded from a series of weight changes were not signif icantly different from the calculated values, 3) the constantly decreasing force exerted by a swinging pendulum placed on the balance was accurately r ecorded, 4) the measurement of activity was not influenced by the evaporati on of a fluid such as urine, and 5) the method can detect differences in th e activity of sleeping and waking rats over a 10-min period, as well as dur ing 4-hr intervals recorded during active (night-time) and inactive (daytim e) periods. These results demonstrate that this method provides an inexpens ive, accurate, and noninvasive method to quantitate the spontaneous activit y of small animals.