Compound action potentials recorded in the ventral tegmental area, substantia nigra, and periaqueductal gray following rewarding stimulation of the lateral hypothalamus in the rat

Neurons activated by rewarding stimulation of the lateral hypothalamus (LH) were studied by two complementary means. To ensure that the same directly stimulated neurons were activated in both tests, the same subjects, stimulation sites, currents, and pulse durations were employed. In the first test, Yeomans’s method was used to obtain behaviorally derived measures of recovery from refractoriness in the neurons responsible for the rewarding effect. In the second test, electrophysiological recording was used to measure recovery from refractoriness in the neurons responsible for compound action potentials (CAPs) evoked by the rewarding stimulation. Refractory-period estimates derived from CAPs recorded in the ventral tegmental area (VTA), substantia nigra (SN), and periaqueductal gray matter (PAG) were found to overlap the refractory-period estimates for the directly stimulated neurons subserving the rewarding effect. These findings reinforce the view that reward-related fibers directly link the LH and VTA, and suggest that fibers similar to those responsible for the rewarding effect link the LH to the SN and PAG.