ABSTRACT
HRP solution (33%) was injected into the left superior colliculus of 21 adult albino rats. 1-2 days after injection, the animal was sacrificed. Brains were frozen sectioned and processed according to. DAB- or TMB-method. The labeled neurones were examined in the right superior colliculus and other areas of the brain. The resu ts are as follows:1. No matter where the HRP was injected (either in the rostral or caudal part of the superior colliculus or thepart between them) HRP labeled neurones were always observed on the opposite superior colliculus if the injection sites reached layers deeper than the stratum oPticum. The locations of the labeled neurones corresponded roughly to the sites of HRP injections. However, no HRP labeled neurones were observed when the core of HRP deposites was restricted to layers superficial to the stratum griseum intermediale.2. Of all labeled neurones, 53.6% were located in the stratum griseum intermediale, 16.5% in the stratum opticum. The rest were in deeper layers. In no case were HRP labeled neurones observed in the stratum zonale or stratum griseum superficiale.3. Labeled neurones could be classified morphologically into vertical fusiform, horizontal fusiform and multipolar neurones.4. In addition to the visual cortex, labeled neurones were also found in the inferior colliculi, paralemniscal nuclei, dorsal nuclei of the lateral lemniscus, substantia nigrae and lateral tegmental nuclei bilaterally. Labeled neurones were also found in the ipsilateral ventral nucleus of the lateral geniculate body, contralatera pretectal area and reticular formation.