The quantitative 2-deoxy[14C]glucose method was used to determine local cerebral glucose utilization in unrestrained rats responding (lever-press) for rewarding electrical stimulation to area A10 (ventral tegmental area) and in similarly implanted inactive controls. Self-stimulation was associated with significant increases in metabolic activity, highly circumscribed in the ventral tegmental area, that continued rostrally within a rather compact zone of activity through the medial forebrain bundle, extending via the diagonal band of Broca to the level of the preoptic area. In the forebrain terminal areas bilateral increases in local cerebral glucose utilization were noted in the nucleus accumbens, lateral septum, hippocampus, and the mediodorsal nucleus of the thalamus. Ipsilateral (i.e., side of stimulation) increases in glucose utilization were noted in the bed nucleus of the stria terminalis, the basolateral and central amygdaloid nuclei, and the medial prefrontal cortex. Caudal to the stimulation site, increases in glucose utilization were found in the midline dorsal raphe, the ipsilateral pontine gray, medial parabrachial nucleus, and the locus coeruleus. Significant bilateral increases were noted in various sensory and motor areas. These results indicate that rather than a diffuse pattern of activity, rewarding brain stimulation is associated with discrete activation of specific neuronal projection fibers and selective terminal sites.The discovery that rats will work to receive brief trains of electrical stimulation to discrete areas of their brains (1) was soon followed by similar demonstrations in diverse species from goldfish to higher primates, including man (2). This phenomenon has generally been interpreted as reflecting a very fundamental neurophysiological mechanism(s) of widespread and adaptive evolutionary significance (3)(4)(5). Early attempts to delineate the critical neural circuitry that mediates the reinforcing or rewarding aspects of this behavior yielded little specific information (6,7). Subsequent studies, however, suggested an important relationship between certain ascending catecholaminergic pathways and this behavior (8, 9). In particular, cogent evidence has been adduced for a critical, albeit nonexclusive, role for ascending dopaminergic fibers in the mediation of self-stimulation derived from cell bodies in the ventral tegmental area (VTA) (9), corresponding to area A10 of Dahlstrom and Fuxe (10). Because of the ability of the 2-deoxy[14C]glucose autoradiographic method to assess local metabolic and functional neural activities simultaneously throughout the entire brain (11), it was used in this study to examine the overall pattern of sensory, motor, and integrative neural activity during rewarding selfstimulation to the VTA.
MATERIALS AND METHODSMale albino Sprague-Dawley rats (-350 g) were anesthetized with chloral hydrate and stereotaxically implanted unilaterally with bipolar platinum electrodes (0.125 mm diameter) aimed at the VTA (coordinates: A + 3.4, L ± 1.0, V + 2....