[14C]Deoxyglucose mapping of first-order projections activated by stimulation of lateral hypothalamic sites eliciting gnawing, eating, and drinking in rats

Abstract

Rats having hypothalamic electrodes that elicited gnawing, eating, and drinking in free-moving tests received intermittent electrical stimulation for 45 min following i.v. injection of [14C] deoxyglucose. Autoradiographs of regional brain glucose utilization were made by the method of Sokoloff et al. ('77). To maximize the detectability of first-order neuronal effects and minimize potentially complex transsynaptic effects, baseline metabolism and synaptic transmission were reduced by light barbiturate anesthesia. Laterally asymmetrical increases in glucose utilization indicative of elicited activity were largely coterminous with the known projections of the lateral hypothalamus and some projections of adjoining areas, indicating that most first-order efferents were above threshold for deoxyglucose visualization, while most transsynaptic effects were subthreshold. Although the majority of hypothalamic projections were similarly affected in control rats that received hypothalamic stimulation that elicited other responses, a number were activated significantly less than in the rats whose electrodes induced gnawing, eating, and drinking. Chief among these areas was a continuous descending pathway from the ventral tegmental area through the lateral tegmentum to the cuneiform and parabrachial nuclei. Smaller and/or less reliable increases above controls were found in the dorsomedial caudate-putamen, the posterolateral zona incerta, the anterior lateral central gray, the caudal linear nucleus, the laterodorsal tegmental nucleus, the pontine tegmental nucleus, and a previously undescribed pathway lying medially between the pontine medial lemniscus and cerebral peduncle. These areas, especially the lateral tegmental and parabrachial zone, are the most likely candidates for the pathways and/or destinations of the directly excited efferents or fibers of passage that constitute the first link in the elicitation of gnawing, eating, and drinking by lateral hypothalamic stimulation. Since self-stimulation and exploratory activity were elicited by control as well as experimental electrodes, they are probably dependent on other projections among those affected similarly in both groups.