NEUROANATOMICAL SUBSTRATE FOR THE DORSAL LIGHT RESPONSE .1. DIFFERENTIAL AFFERENT CONNECTIONS OF THE LATERAL LOBE OF THE VALVULA-CEREBELLI IN GOLDFISH (CARASSIUS-AURATUS)

The afferent connections of the lateral lobe of the valvula cerebelli in goldfish were investigated by retrograde labeling with horseradish peroxidase (HRP). Retrogradely labeled neurons were observed ipsilaterally in the lateral nucleus of the valvula and contralaterally in the inferior olivary nucleus after HRP injection into all parts of the lateral valvula. The valvulopetal projections from these nuclei were topographically arranged. After HRP injection confined to the rostral half of the lateral valvula, labeled neurons were also found ipsilaterally in the octavolateral and trigeminal cell groups: the eminentia granularis, the medial nucleus of the octavolateralis column, and the isthmic primary sensory trigeminal nucleus. HRP injection confined to the caudal half of the lateral valvula resulted in retrograde labeling of the following vision-related cell groups; the central pretectal nucleus, nucleus paracommissuralis, and the nucleus isthmi. However, the octavolateral and trigeminal cell groups did not project to the caudal half of the lateral valvula. These data provide insight into central nervous integration of visual and vestibular information, and help reveal the mechanism of the dorsal light response (DLR). Bilateral lesions of either the valvula cerebelli or pretectal area completely abolish this visually-guided response, but lesions of the optic tectum have no such effect. The pretectal nuclei (central pretectal nucleus, nucleus paracommissuralis) project to the lateral valvula directly, not via the optic tectum. These direct projections from the pretectal accessory optic nuclei to the lateral valvula may control the DLR. On the other hand, the lateral valvula receives vestibular and lateral line inputs indirectly, via the eminentia granularis and the medial nucleus of the octavolateralis column, respectively. These findings indicate that the lateral valvula is probably responsible for visual-vestibular interactions such as those required for the DLR.