Quantifying operant behavior deficits in rats with bilateral 6-hydroxydopamine lesions of the ventrolateral striatum

The present study examined the effects of bilateral 6-hydroxydopamine lesions in the ventrolateral striatum on the operant behavior of rats. Use of the specially modified operant chambers allowed the measurement of forelimb response force and duration as well as the time intervals between selected behavior in the press-consume-press sequence. More specifically, four time intervals between separate behavioral events were measured: 1) the time from the end of forelimb response to entry of muzzle into the reinforcement well, 2) the time from muzzle entry to the first tongue lick of the water reinforcer; 3) the time from the last lick to muzzle withdrawal from the reinforcement well, and 4) the time from muzzle withdrawal to the beginning of the next forelimb operant response. As determined by neurochemical (HPLC) analysis, the lesioned group exhibited dopamine levels that were 35% of the control group. The operant behavioral deficits were most profoundly appeared in the first week of postoperative test. Behaviorally, the lesioned group exhibited longer forelimb response durations (bradykinesia), and decrements were seen in both the number of muzzle entries and the number of recorded licks during reward consumption. Furthermore, the lesion significantly increased the average latency to switch from the forelimb response to the entry of the muzzle into the reward well. The latency from well entry to the first tongue extension to the reward was also increased by the lesion. These data support the view that the rodent neostriatum is important in the control of behavioral sequences for psychomotor function and at the same time demonstrate the utility of new quantitative behavioral methods for investigating such functions.