Electrical self-stimulation of the mesencephalic central gray area: facilitation by lateral hypothalamic stimulation

Three experiments were performed with BALB/c mice implanted both in the lateral hypothalamus (LH) and the dorsal part of the mesencephalic central gray area (CG). Initially, the effects of a brief electrical stimulation (0.2 sec) of the LH on approach and escape responses produced by continuous stimulation of the dorsal CG, were studied in a shuttle-box. Starting at an intensity of 10 microA, imposed LH stimulation both reduced approach latency and increased escape latency with CG stimulation. In the second and third experiments, the animals were placed in a standard self-stimulation (ICSS) box; depressions of a lever delivered brief electrical stimulations (0.2 sec). During the second experiment, it was observed that the very weak ICSS behavior produced by dorsal CG activation was greatly improved by forced LH stimulation. Finally, in the third experiment, simultaneous ICSS in LH and CG was compared with ICSS in LH alone. When low current intensities were used, simultaneous ICSS in LH and CG was more intense than ICSS in LH alone. These data especially suggest that dorsal CG stimulation has an appetitive component, and consequently that neuronal elements related to the positive reinforcement system are present in the dorsal CG area. Furthermore, the fact that one can obtain interactions between mesencephalic and hypothalamic ICSS is in accordance with the claim that the LH has connections with the CG area.