Abstract

This study was conducted to determine whether lateral hypothalamus (LH) per se or dopaminergic fibers which originate in substantia nigra (SN) and pass through LH serve to facilitate responsiveness to external stimuli. For this, rats were trained to respond to a visual cue presented on the left or night side of front panel of a chamber. The cue signaled availability of brain stimulation reward. The rats were then subjected to two kinds of preference test. In one test cues were simultaneously presented in both sides, and in another presented in neither side. With this procedure, rats were tested while they were unilaterally self-stimulating SN. The rats were retested after the lesion of LH with kainic acid which is selective neurotoxin to neuronal perikarya. When SN was unilaterally stimulated, rats responded more to the visual cue presented on the side contralateral to brain stimulation than ipsilateral. Even if cell bodies of LH were lesioned, this effect was not affected. The results may be interpreted as an indication that nigrostriatal dopamminergic system which transverses LH rather than LH per se is concerned with sensorimotor functions.