Locomotor sites mapped with low current stimulation in intact and kainic acid damaged hypothalamus of anesthetized rats

Abstract

To determine whether local neurons mediated the locomotor effects of electrical stimulation of the lateral hypothalamus, kainic acid injections (0.5-1.25 micrograms), intended to destroy neural somata as opposed to fibers of passage, were made unilaterally in the tuberal-posterior hypothalamus of 22 rats. The area of lesion and its contralateral homolog were mapped for locomotor stepping sites in Nembutal-anesthetized rats mounted in a stereotaxic apparatus such that locomotor stepping rotated a wheel. Stimulation (25 and 50 microA, 50 Hz, 0.5-ms cathodal pulses, 10-s trains) was delivered through 50-80 microns glass pipettes filled with 2 M saline. Contralateral to the lesion, locomotor stepping sites were common in the perifornical lateral and medial hypothalamus and less dense in the zona incerta. On the side of the kainic-acid lesion, locomotor sites were generally absent in the central part of the damaged area. If they did appear within the area of lesion, they tended to be near the border with intact tissue. In a few cases, locomotor stepping sites were found centrally located in the lesion amidst widespread loss of somata. In four rats, additional maps of anterior locomotor regions in the preoptic area ipsilateral to the lesion suggested that their descending fibers were largely spared by the kainic lesions. Local neurons appear to be major contributors to the locomotion elicited by electrical stimulation of the lateral hypothalamus, but fibers of passage may also participate.