Functional participation of the valvula cerebelli on the goldfish dorsal light response.

Most fish swim freely in three dimensions. The vestibular organs of fish are well developed and play an important role in maintaining postural equilibrium. Postural equilibrium in teleost fish also depend on visual information. Dorsal light response (DLR) of fish has been well-known as representative visually guided behavioral response since von Holst's description in 1935. The DLR, an innate behavior of teleost fish, whereby the back is oriented toward a given light source, represents a simple interaction between the visual and vestibular sensory inputs. In order to identify the neural center of the DLR in goldfish, lesion studies of the goldfish brain were conducted in our laboratory. The DLR was not affected by the extirpation of the corpus cerebelli, but was entirely abolished after bilateral lesions of the valvula cerebelli. The valvula cerebelli in goldfish was separated into the medial and lateral lobes by a longitudinal fissure. As to the afferent connections of the corpus cerebelli, many findings have been reported. However, the function and the fiber connections of the valvula cerebelli, especially its lateral lobe, are still unknown. Therefore, we examined the afferent connections of the lateral lobe of the valvula cerebelli by means of tracing technique with horseradish peroxidase. Furthermore, we investigated the effects of selective lesions of the medial and lateral valvula cerebelli on the DLR.