Deeply anesthetized rats (see above; n=6 in each group) were placed in a stereotactic apparatus (Stoelting, Kiel, Germany), and the skin overlying the skull was cut open. The lambda and bregma sutures served as landmarks for drilling four holes. FG (Biotium, Hayward, CA) was injected (8 μl of 4% FG in distilled H2O) in the superior colliculus and lateral geniculate bodies [20 (link)-22 (link)]. To allow for the retrograde transport of FG, the animals were kept for 6 days before further experimentation.