[Retinotectal and tectopontine projection in the guinea pig: experimental, anatomical and electrophysiological study]

The collicular organization of mammals such as the rabbit, cat, and monkey have been well studied. However, little anatomical or physiological information about the guinea pig has been available. Consequently, the author studied the descending and ascending projections of the superior colliculus in the guinea pig by using both anterograde horseradish peroxidase conjugated with wheatgerm agglutinin (WGA-HRP) tracing and electrophysiological techniques, and the following results were obtained. 1. Evoked potentials were recorded from the superior colliculus contralateral to the site of photic stimulation of the retina. Recordings from the superficial layer of the superior colliculus displayed negative waves, whereas recording from the deeper layer displayed positive waves. 2. After intraocular injection of WGA-HRP, anterograde labels were observed in the stratum griseum superficiale and stratum opticum of the superior colliculus contralateral to the injection site. 3. Eye movements with deviation toward the upward or contralateral side were elicited by electrical stimulation in the intermediate layer of the superior colliculus. 4. After injection of WGA-HRP into the superior colliculus, transported labels were observed in the dorsolateral basilar pons ipsilateral to the injection site, and the paramedian pontine reticular formation contralateral to the injection site. These studies suggested that the pathway through the superior colliculus observed in the guinea pig is similar to that in other mammals. However, some differences may exist with respect to the processing of light signals and the mechanism causing eye movement.