Fig. 19.

The schematic diagram summarizes the present findings and those of previous studies. We found that the main projection from the PT to the PUL is an ipsilateral, non–γ-aminobutyric acid (GABA) -ergic projection. The PT-PUL neurons are primarily located within the NOT (open circles) and are presumably identical to the “jerk” cells receiving retinal input from Y ganglion cells (Ballas and Hoffmann, 1985). The non-GABAergic PT-PUL terminals form large clustered boutons in the PUL and contact both thalamocortical cells (open circles) and interneurons (filled black circles). We also found that both the ipsilateral and contralateral PUL receives a diffuse GABAergic projection from presumably another set of pretectal neurons (filled gray circle), the “saccade” cells. These GABAergic terminals form smaller, beaded boutons that likely branch to bilaterally innervate the PUL and dLGN. In the dLGN, they contact mostly interneurons (filled gray circles), whereas in the PUL they contact both thalamocortical cells and interneurons. For abbreviations, see list.