Tectal projection neurons to the retinopetal nucleus in the filefish

Following horseradish peroxidase (HRP) injections into the preoptic retinopetal nucleus (PRN), neurons in the ipsilateral optic tectum were labeled retrogradely. Labeled neurons exhibited a 'Golgi-like' appearance, somata of these neurons were pyriform or round, and most of them were located in the stratum album centrale (SAC) or the stratum periventriculare (SPV). These neurons had a long apical dendrite, which ramified in the upper-half of SGC into horizontally arborized dendritic fields. The main trunk of the apical dendrites also gave off several branches in the stratum fibrosum et griseum superficiale (SFGS) and reached the stratum opticum (SO). These neurons resemble the 'large pyriform neurons' of Vanegas et al. (Vanegas, H., Laufer, M. and Amat, J., The optic tectum of a perciform teleost. I. General configuration and cytoarchitecture, J. Comp. Neurol., 154 (1974) 43-60) except that in the tecto-PRN neurons the axons originates from the apical dendritic shaft at or near the level of the SAC. Judging from their dendritic patterns, the tectal neurons projecting indirectly to the retina may receive non-retinal inputs besides the retinal input.