Chemoresponsiveness of intracerebellar nuclei neurones to l-aspartate, l-glutamate and related derivatives in rat cerebellar slices maintained in vitro

Abstract

The sensitivity of intracerebellar nuclei neurones to pulse applications of l-aspartate. l-glutamate, N-methyl- d,l-aspartate and quisqualate was tested in rat cerebellar slices mainlained in vitro. The responses ol the nuclear neurones to the four agonists consisted of a transient and dose-dependent increase in their firing of simple spikes. When suprathreshold currents were used, quisqualate induced the highest increase in the spike discharge frequency of the cells. Quisqualate mediated responses were unaffected by steady applications of 2-amino-5-phosphonovalerate. whereas the sensitivity of the responses induced by the three other agonists was in the order N-methyl- d,l-aspartate. l-aspartate. l-glutamate. When the supervising solution was devoid of Mg 2+ ions. N-methyl- d,l-maspartate and l-aspartate mediated responses were much potentiated, while quisqualate induced responses were not enhanced. In such a medium, l-glutamate elicited responses were more or less potentiated depending on cells. These results suggest that rat intraeerebellar nuclei neurones hear both N-methyl- d-aspartate and non- N-methyl- d-maspartate. probably quisqualate. receptors, and that laspartate and l-glutamate have a mixed action upon both types. l-Aspartate preferentially activates N-methyl- d-aspartate receptors, whereas l-glutamate predominantly acts via non- N-methyl- d-aspartate receptors, Furihermore, the potency of l-glutamate in activating N-methyl- d-aspartate receptors appears to vary as a function of the cells.