Hypothalamic self-stimulation in rats with one hemisphere isolated anterior to the midbrain and the other hemisphere devoid of the telencephalon.

The telencephalon was removed unilaterally in rats. In addition, the forebrain of the other hemisphere was isolated from its brain stem by a precollicular transverse cut. This preparation was then tested for self-stimulation via electrodes implanted in the region of the lateral hypothalamus and medial forebrain bundle (LH-MFB) of either hemisphere. Self-stimulation was found to be intact in both hemispheres. Possible pathways connecting the LH-MFB region of one hemisphere to the contralateral diencephalon were also investigated in the bilaterally detelencephalized rat. The technique of retrograde transport of horseradish peroxidase was used for this purpose. Some fibers from the LH-MFB of one hemisphere were found to decussate to the other hemisphere by way of the thalamic commissure. The supraoptic decussation as well as diffusely organized interdiencephalic connections provide additional routes for interhemispheric LH-MFB projections.