Differential hypothalamic self-stimulation behaviour in Roman high-avoidance and low-avoidance rats.

Monopolar electrodes were implanted bilaterally and symmetrically into a small well defined region of the posterior lateral hypothalamus in 11 rats of the selected strains Roman high-avoidance (RHA/Verh, 6 animals) and Roman low-avoidance (RLA/Verh, 5 animals). Intracranial electrical stimulation (ICS) was used to study possible strain difference with respect to self-stimulation behaviour. Using a shuttle-box, the experimental set-up allowed measurements of the animal's preference, aversion, neutrality or ambivalence towards the stimulus. For both rat strains 10 electrode sites were tested with identical stimulation currents (100-600 microA in increments of 100 microA). Significant differences between the selected strains were found for preference (self-stimulation) and aversion: RLA/Verh-rats showed self-stimulation at lower stimulation currents than RHA/Verh-rats. At higher currents, both strains showed similar self-stimulation performance. RLA/Verh-rats escaped more often from ICS yielding self-stimulation at five of the six current levels. It is concluded that, in comparison with the RHA strain, RLA/Verh-rats are more sensitive to aversive effect of lateral hypothalamic stimulation. This seems to be associated with an increased sensitivity to the rewarding effects of such stimulation.