Divergent axon collaterals from the rostral superior colliculus to the pretectal accommodation-related areas and the omnipause neuron area in the cat.

Results of previous studies have suggested that the rostral superior colliculus (SC), which corresponds to the representation of the central visual field, is involved in the control of accommodation and active fixation. To clarify the functional interaction between accommodation and active fixation in the rostral SC, this study was performed to investigate the axon collaterals diverging from the rostral SC to the pretectal accommodation-related areas and the omnipause neuron area in the raphe interpositus (RIP) of the cat by using a fluorescent double-labeling technique. This study was conducted on four cats, weighing 2.5-3.5 kg. Retrogradely labeled neurons in the SC were examined following injections of Fast Blue into the RIP and Diamidino Yellow into the pretectal accommodation-related areas, which were identified with microstimulation techniques. Neurons projecting to the RIP were located mainly in the intermediate layers in the rostral SC, whereas neurons projecting to the pretectal accommodation-related areas were scattered in the superficial and intermediate layers of the rostral SC. The population of double-labeled neurons was highest in the rostral SC, which corresponds to the representation of the central visual field. The presence of double-labeled cells indicated that the accommodation-related area in the rostral SC contains neurons whose axons collateralize to project to both the pretectal accommodation-related areas and the ominipause neuron area in the RIP. Neurons in the rostral SC may be involved in the interaction between accommodation and active fixation. Copyright 1999 Wiley-Liss, Inc.