6-Hydroxydopamine treatment enhances excitation of cultured cerebellar neurons by glutamate

Abstract

Explant cultures containing identifiable cerebellar cortical neurons and locus coeruleus neurons were treated with 500 μM 6-hydroxydopamine. At this concentration, locus coeruleus neurons were usually degenerated after 48 h, while the cerebellar cortical neurons had a normal appearance. Extracellular recording and iontophoresis of noradrenaline and glutamate were used to test for changes in electrical activity or neurotransmitter responsiveness of the cerebellar neurons. At 4–5 days following the toxin exposure, spontaneous spiking activity appeared similar to that in control cultures. Mean iontophoretic currents required to give noradrenaline-induced depressions of activity were somewhat lower for the toxin-treated cultures than for controls but not significantly so. The mean currents for glutamate excitations, however, were markedly lower in the treated cultures. Noradrenaline potentiations of glutamate responses were observed in both treated and control cultures. The greatly increased sensitivity of cerebellar neurons to glutamate does not seem related to degeneration of granule cells in the treated cultures but might be explained by disruption of astrocytic uptake mechanisms for glutamate.