Retinofugal projections of an echolocating megachiropteran.

Abstract

AbstractThe projection leading from the eye and the nuclear targets of the projection to the brainstem were identified in an echolocating megachiropteran (Rousettus aegyptiacus) following unilateral intraocular injections of radioactive amino acids. In the hypothalamus, the projection ended bilaterally in suprachiasmatic nuclei. In the ventral thalamus, it ended bilaterally in external and internal divisions of the ventral lateral geniculate nuclei. In the dorsal thalamus, the projection terminated bilaterally in the dorsal lateral geniculate nuclei and contralaterally in the lateral posterior nucleus. Input from the two eyes was segregated to laminae in the lateral division of the dorsal lateral geniculate nucleus. The contralateral projection ended in the dorsolateral and ventral portions of lamina 1, in lamina 2, the ventral portions of lamina 3, and an interlaminar fiber plexus. The ipsilateral projection ended in the dorsomedial portion of lamina 1, the dorsal portion of lamina 3, and the most superficial portion of lamina 1. Contralateral and ipsilateral input to the medial division of the dorsal lateral geniculate nucleus was for the most part segregated. The projection to the pretectum terminated in nuclei of the optic tract, pretectal olivary nuclei, and posterior pretectal nuclei. Although the input to the pretectal nuclei was bilateral, the contralateral projection was greater. The contralateral projection to the superior colliculus terminated throughout the rostral‐caudal extent of the superficial gray layer. The ipsilateral projection to the superior colliculus ended in the superficial gray layer in the middle one‐third of the superior colliculus only. On the contralateral side the projection to the outer portion of the superficial gray layer was especially heavy. The superior fascicle of the accessory optic tract was identified. It was traced to dorsal, lateral, and medial accessory optic nuclei. These results indicate that the visual system of Rousettus is more extensive than that of the echolocating microchiroptera and that it is similar to that described for nonecholocating Pteropus.