Excitatory synaptic potentials in neurons of the deep nuclei in olivo-cerebellar slice cultures

Excitatory postsynaptic potentials evoked in neurons of the deep cerebellar nuclei, either by electrical stimulation within the nuclei in cerebellar slice cultures or by electrical stimulation of olivary explants in olivo-cerebellar co-cultures, were investigated in the rat by means of intracellular recordings. In neurons of the deep cerebellar nuclei, stimulation of the nuclear tissue, as well as stimulation of the olivary tissue, induced a fast rising excitatory postsynaptic potential, followed by an inhibitory postsynaptic potential and a long-lasting excitation. The fast rising excitatory postsynaptic potential and the following inhibitory postsynaptic potential were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione. The remaining depolarization was abolished by d-(−)-2-amino-5-phosphonovalerate, suggesting that this potential was mediated by N-methyl-d-aspartate receptors. With only d-(−)-2-amino-5-phosphonovalerate added to the bath, the slow excitation was depressed, whereas the fast excitatory and inhibitory postsynaptic potentials were not affected. In the presence of bicuculline, the 6-cyano-7-nitroquinoxaline-2,3-dione- and the d-(−)-2-amino-5-phosphonovalerate-sensitive excitatory postsynaptic potentials elicited by stimulation of the olivary tissue had the same latency, and were both graded with stimulation strength. The time-to-peak and the duration of the d-(−)-2-amino-5-phosphonovalerate-sensitive excitatory postsynaptic potentials were considerably longer than those of the 6-cyano-7-nitroquinoxaline-2, 3-dione-sensitive excitatory postsynaptic potentials. In magnesium-containing bathing solution, the amplitude of the 6-cyano-7-nitroquinoxaline-2,3-dione-sensitive excitatory postsynaptic potentials increased, while the amplitude of the d-(−)-2-amino-5-phosphonovalerate-sensitive excitatory postsynaptic potentials decreased with membrane hyperpolarization. Removal of magnesium from the bathing solution resulted in an increase in N-methyl-d-aspartate receptor-mediated excitatory postsynaptic potentials whose amplitude increased with membrane hyperpolarization.

Recordings from Purkinje cells within the same slice cultures revealed that 6-cyano-7-nitroquinoxaline-2,3-dione reversibly abolished graded excitatory postsynaptic potentials induced by stimulation within the cerebellar cortex as well as all-or-none climbing fibre responses induced by stimulation of the olivary tissue. Furthermore, d-(−)-2-amino-5-phosphonovalerate did not affect these synaptic responses, even in magnesium-free bathing solution.