'Disengage' sensorimotor deficit following apparent recovery from unilateral dopamine depletion

Sensorimotor behavior in Long-Evans rats was evaluated acutely and chronically after unilateral dopamine depletion caused by infusions of 6-hydroxydopamine into the nigrostriatal system. In each rat, control infusions were delivered to the opposite hemisphere and a noradrenaline uptake blocker was used as a pretreatment to help protect noradrenaline cells. During the first few postoperative weeks, head movement reactions to repetitive tactile-perioral stimulation contralateral to the dopamine-depleted hemisphere were delayed but not eliminated. With recovery, facilitated by special training, the rats were able to respond quickly. However, two lasting abnormalities were observed. First, the types of head-orienting movements directed toward contralateral stimulation were different from that directed toward ipsilateral stimulation. Second, when the animals were engaged in eating behavior there was a complete failure to orient to contralateral stimulation, whereas they instantly disengaged from eating to orient to ipsilateral stimulation. When not eating, orienting was rapid and reliable to stimulation of either side of the body. These data may have implications for the role of the striatum and connected structures in the organization and integration of sensorimotor and ingestive behavior.