An improved circular tilt-cage shows that intrahypothalamic injections of sulpiride increase locomotion

A circular tilt-cage was designed and constructed to measure locomotor activity in rats. Some improvements in relation to previously described circular tilt-cages, as the easy calibration and the automation of the data collection, were introduced. The detection system was built interfacing the actimeters through a circuit board to a Casio FP-200 computer. The interface, the computer and the software can be used to count lever presses or other kind of switch closures. This apparatus was used in the present report to quantitate the locomotor activity induced by sulpiride injected in the perifornical region of the lateral hypothalamus. Bilateral injections of sulpiride (8 micrograms/0.5 microliters) increased locomotion immediately after the injections and for the next 75 min. Bilateral amphetamine (20 micrograms/0.5 microliters) did not change activity. Several doses of sulpiride (2, 4, 8, and 16 micrograms/0.5 microliters) increased activity in a dose-dependent fashion. These results are discussed in terms of the existence of postsynaptic D2 receptors in the lateral hypothalamus involved in inhibition of locomotion.