Fig. 1.

Identifying the PAG homologue. (A) Injection of Neurobiotin into the pretectum. (B–C) Bilaterally located retrogradely labeled cell body clusters in the periventricular area in the ventromedial mesencephalon. The squared area in B is shown in high magnification in C. (D) Injection of Neurobiotin into the SNc, confirmed by the presence of tyrosine hydroxylase (TH) immunoreactive cells (red). (E) High magnification photomicrograph of retrogradely labeled cell bodies (green) located periventricularly in the ventromedial mesencephalon with TH immunopositive fibers (red) in close proximity to the cells. (F and G) In situ hybridization of the dopamine D1 and D2 receptor transcripts showing expression of the dopamine D1 (F) and the D2 (G) receptor, respectively, in griseum centrale,. (H) Retrogradely labeled cells (green) in the griseum centrale following SNc injection (D) combined with 5-HT immunohistochemistry. (I) 5-HT immunoreactive fibers (red) in close proximity to the retrogradely labeled cells (green; high magnification photomicrograph of the squared area in H). All sections were counterstained with a fluorescent Nissl stain. 5-HT, serotonin; M1, Müller cell 1; M3, Müller cell 3; nIII, oculomotor nerve; IPN, interpeduncular nucleus; TH, tyrosine hydroxylase. Scale bars = A, B, D, F, G, H, 250 μm; C, E, I, 50 μm. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)