A new device for the simultaneous measurement of locomotor and stereotypic frequency in mice

Abstract

The ability of a new apparatus to measure simultaneously and objectively both locomotor activity and stereotypy induced in individual mice by d-amphetamine, morphine, cocaine, and methylphenidate was compared with commonly used visual observational scoring procedures. The basis for the differential quantifying capacity of the apparatus resides in two capacitative sensors which respond to animal-induced changes of a tuned resonating capacitive field. The responses of the capacitive sensors produce voltage pulses proportional to the amplitude of animal movement. These pulses are then counted. High sensitivity measurement (total counts) recorded such movements as licking and grooming as well as movements of greater body mass (locomotion). Respiration was not recorded. Low sensitivity measurement (locomotor counts) recorded only movements of relatively greater body mass such as locomotion and rearing onto hind legs. Stereotypic activity was defined as total counts less locomotor counts. Changes induced by cocaine, methylphenidate, and morphine in locomotor and stereotyped behaviors measured electronically agreed closely with the results of the observational scoring procedures. When measured by machine the d-amphetamine dose-response data also compared well with the observational results, except at the highest dose (32 mg/kg). This dose of d-amphetamine induced extreme stereotypy of sufficient amplitude to be recorded as locomotor activity by the apparatus. The results indicate that the expanded behavioral measurement capabilities of this apparatus offer several advantages over previous related measurement techniques.