The neuronal organization of a unique cerebellar specialization: The valvula cerebelli of a mormyrid fish

Abstract

The distal valvula cerebelli is the most prominent part of the mormyrid cerebellum. It is organized in ridges of ganglionic and molecular layers, oriented perpendicular to the granular layer. We have combined intracellular recording and labelling techniques to reveal the cellular morphology of the valvula ridges in slice preparations. We have also locally ejected tracer in slices and in intact animals to examine its input fibers. The palisade dendrites and fine axon arbors of Purkinje cells are oriented in the horizontal plane of the ridge. The dendrites of basal efferent cells and large central cells are confined to the molecular layer, but are not planer. Basal efferent cell axons are thick, and join the basal bundle leaving the cerebellum. Large central cell axons are also thick, and traverse long distances in the transverse plane, with local collaterals in the ganglionic layer. Vertical cells and small central cells also have thick axons with local collaterals. The dendrites of Golgi cells are confined to the molecular layer, but their axon arbors are either confined to the granular layer or proliferate in both the granular and ganglionic layers. Dendrites of deep stellate cells are distributed in the molecular layer, with fine axon arbors in the ganglionic layer. Granule cell axons enter the molecular layer as parallel fibers without bifurcating. Climbing fibers run in the horizontal plane and terminate exclusively in the ganglionic layer. Our results confirm and extend previous studies and suggest a new concept of the circuitry of the mormyrid valvula cerebelli.The cerebellum is an important brain structure in almost all vertebrate groups, reaching its relatively largest size and differentiation in fishes, birds and as in mammals (Nieuwenhuys et al., 1998). Throughout the diverse vertebrate radiation the cerebellum has maintained a strikingly consistent and regular structure and organization, including 1) the existence of The cutting chamber was filled with ice-cold ACSF and equilibrated with 95% O 2 and 5% CO 2 during slicing. Up to this point, the ACSF contained the nonselective glutamate Shi et al. Interestingly, the widths of dendritic trees vary markedly from rostral to caudal. To quantitatively evaluate such variability, the widths of dendritic trees were measured from Shi et al. Fig. 12. Morphology and physiology of a Golgi-like cellA. A Golgi-like cell labeled with fluorescent dye in a transverse slice, as shown schematically in the insertion. The characteristic morphological feature of this cell is the way its axon arbors project into both the granular layer (gran) and the ganglionic layer (ggl). B. Similar to Golgi cell shown in Fig. 11, this Golgi-like cell fired a single type of spikes with adaptation in response to a somatic current injection of 200 pA (left), and responded to stimulation of molecular layer (SM) with an EPSP under current clamp (right). Summary diagram, showing the cell types and their connections identified in this study. Opened circles represent excitatory terminals, filled...