Wheel-running of rats in combination with a simple self-stimulation procedure

LONG EVANS hooded rats with chronically implanted electrodes in the Area hypothalamica lateralis (AHL, group 1), the Nucleus linearis rostralis (LR, group 2) and the Nucleus centralis superior (CES, group 3) were offered the possibility to spontaneously perform wheel-running for one hour per session. The number of wheel revolutions per ten minutes and per hour were counted automatically. The rats were connected with a square wave generator by a smooth flexible cable and received stimulus series (50 imp./s; 0.5 ms imp. duration; 0.5 s series duration; 0-3 V intensity) triggered by each complete revolution of the wheel. The sessions took always place at the same time of the day and under the same experimental conditions -- except the change of stimulus intensity. The results with 0 V served as controls. The method has the following advantages: 1. Self-stimulation is induced spontaneously in the first stimulation session. 2. Negative emotional effects can be quantified by the decrease of the wheelrunning activity. -- AHL stimulation caused an increase in the wheel-running activity amounting to 300-350% with a maximum at 3 V. LR stimulation brought about an ambivalent effect with increase to 200% at 1-2 V and decrease to 56% at 3 V. During CES stimulation an increase to 166-240% with its maximum at 2 V was observed. Stimulation with the same parameters did not evoked locomotion in an open field situation.