[Retinal projections to the pretectum in the fowl (Gallus gallus domesticus)]

The retinal projection to the pretectum was examined in the adult domestic fowl by means of anterograde transport of horseradish peroxidase (HRP). At the same time, the cytoarchitecture of the pretectum was studied in Nissl preparation. Fifteen fowls (Gallus gallus domesticus) were used for the HRP study, and four were used for the cytoarchitectural study. One hundred microliters of a 30% HRP solution in physiological saline were injected into the vitreous body of the unilateral eye under sodium pentobarbital anesthesia (30 mg/kg body weight). After a postoperative period of 48 hours, the animals were deeply anesthetized and perfused intracardially with 1,000 ml of Ringer solution, followed by 2,000 ml of 1% paraformaldehyde and 1.25% glutaraldehyde in a 0.1 M phosphate buffer (pH 7.4) which was then followed by 1,000 ml of 10% sucrose in the same buffer. The brain was cut into serial transverse sections at 60 microns on a freezing microtome. Every section was treated with tetramethyl benzidine (TMB). Based on cytoarchitectural and HRP results, the pretectum of the adult hen was divided into the following eight nuclei: nucleus principalis pretectalis (P), nucleus subpretectalis (SP), nucleus principalis precommissuralis (PPC), nucleus medialis pretectalis (PTM), nucleus pretectalis dorsalis (APd), nucleus area pretectalis (AP), nucleus spiriformis lateralis (SPL), and nucleus spiriformis medialis (SPM). The SPL and SPM lay closely adjacent to each other, although the boundary between them can be easily defined in any section. Furthermore, the SPM could be divided into two subnuclei: the dorsal part of the SPM (SPMd) located just under the SMT and dorsomedial to the P, and the ventral part of the SPM (SPMv), which was located above the PPC and ventromedial to the P. Retinal projections were found in the APd, the PTM, the AP and the SPM, contralaterally. APd was the smallest nucleus among the pretectal nuclei lying just above the tractus septomesencephalicus (SMT) and received the heaviest retinal inputs. In the PTM, clear terminals were distributed over the whole of the nucleus, whereas strong labeled terminals were also found around the principal pretectal nucleus. Slight retinal inputs were found in the ventral part of the SPM. Furthermore, heavily labeled terminals were found in the medial part of the AP designated as the interstitial nucleus of the posterior commissure by Niimi. Terminals in the ventral part of the SPM and the medial part of the AP have not been reported in the previous studies in the chick and pigeon. There were no terminals in the contralateral P, SPL, SP, PPC, and the ipsilateral brain stem.