l‐Aspartate and l‐glutamate binding sites in developing normal and ‘nervous’ mutant mouse cerebellum

Abstract

This study concerns the ontogeny and the cellular localization of l-aspartate and l-glutamate binding sites in normal and ‘nervous’ mutant mouse cerebellar membranes. The binding kinetics revealed for l-aspartate a single binding system (K_d = 750 nM) and for l-glutamate also a single binding component of higher affinity (K_d = 344 nM). The pharmacological study, using various amino acid analogues, revealed a differential specificity for the binding sites of the two amino acids. The developmental study showed that the binding sites of both amino acids appear mainly during the second and third week of life, a period when parallel and climbing fiber synaptogenesis occurs, but they follow a slightly different developmental pattern. The study using ‘nervous’, mutant mouse cerebellum showed an age-dependent decrease of l-aspartate and l-glutamate binding, which coincides in time with the Purkinje cell degeneration in this mutant, indicating a cellular localization of these binding sites on the Purkinje cell membranes. These results suggest that l-aspartate and l-glutamate binding sites may be respectively associated with the postsynaptic target of climbing and parallel fibers on the Purkinje cell dendrites. However, the decrease of specific binding in ‘nervous’ mutant mouse cerebellum was about 50% for l-aspartate and 60% for l-glutamate, implying that a significant number of l-aspartate and l-glutamate binding sites are located on cerebellar elements other than the Purkinje cell membranes.