Anatomical substrate of amphibian basal ganglia involvement in visuomotor behaviour

The optic tectum of amphibians is known to play a major role in the control of visually elicited orienting movements, such as prey-catching and avoidance behaviours. The recent finding of a direct striato-tectal connection in the frog Rana perezi prompted us to study in detail the anatomical substrate by which the basal ganglia of amphibians may modulate visuomotor behaviour. Injections of anterograde tracers into the striatum were combined with applications of retrograde tracers in the mid-brain tectum. Apart from a direct striato-tectal connection, at least three indirect pathways were observed, viz. a striato-anterior entopeduncular-tectal pathway, a striato-pretectal-tectal pathway and a striato-tegmento-tectal pathway. The basal ganglia-tectal connections of anurans largely resemble those described for amniotes, but appear to be more extensive. However, a pallio-tectal connection comparable to the cortico-tectal pathways of mammals was not observed in Rana perezi. Therefore, the striatum of anurans, which receives multimodal sensory information, seems to be the sole telencephalic structure that influences the mesencephalic tectum via a direct pathway.