Lateral subthalamic area as mediator of classically conditioned bradycardia in rabbits

This study was conducted to examine whether a central efferent pathway passing through the lateral zona incerta (LZI) of the subthalamus selectively mediates the bradycardia conditioned response (CR) in rabbits. Electrodes were implanted bilaterally in LZI or in control sites just dorsal or ventral to LZI. Two days following surgery, animals were subjected to Pavlovian conditioning or to pseudoconditioning. Subsequent bilateral electrolytic lesions did not influence the heart rate (HR) orienting response, unconditioned response, baseline, or lack of response to pseudoconditioning. Bilateral LZI lesions alone abolished the HR CR. In a follow-up experiment, the corneoretinal potential (CRP) CR and HR were recorded. Bilateral LZI lesions following conditioning to a criterion of 65% CRP CRs abolished the HR CR without affecting CRP CRs. The present findings indicate that LZI is part of an efferent pathway that selectively mediates the HR CR in rabbits.