Teleost fish

Abstract

Teleost fish have the largest number of species among vertebrates. The basic structure of the central nervous systems is conserved from mammals to teleosts, including the cerebellum. The cerebellum of teleost fish is subdivided into three parts: corpus cerebelli, valvula cerebelli, and vestibulolateral lobe (including eminentia granularis and lobus caudalis). Although the anatomical features, including the layer structure and the cellular organization, of the teleost cerebellum are shared with other vertebrates, there are some exceptions. One of them is the lack of the structure corresponding to the deep cerebellar nuclei. Instead, the teleost cerebellar efferent neurons do not form clusters and are distributed within the ganglionic layer, equivalent to the Purkinje cell layer of other vertebrates. These efferent neurons project their axons to other brain regions using an excitatory neurotransmitter. According to this character, it could be said that the teleost cerebellar efferent neurons are functionally analogous to the neurons of the deep cerebellar nuclei. However, they have dendrites extending to the molecular layer like the Purkinje cells, indicating that they receive inputs from parallel fibers unlike the neurons of the deep cerebellar nuclei. These neurons are unique in the teleost cerebellum, and it is important to understand their details to evaluate the function of the teleost cerebellum. Although the existence of basket cells has still not been described, the teleost cerebellum possesses intracerebellar neurons of kinds similar to those of other vertebrates and their connectivity and neurotransmitters are also similar. The afferent and efferent fiber connection patterns suggest that the basic function of the teleost cerebellum is similar to that of other vertebrates, but each subdivision of the teleost cerebellum is functionally separate. In the last decade, the functional role of the teleost cerebellum was reevaluated with some physiological and behavioral experiments, and it was revealed that the teleost cerebellum has an important role for the execution of swimming gait, controlling the vestibulo-ocular reflex, and emotional learning.