PREGNENOLONE SULFATE INCREASES GLUTAMATE RELEASE AT NEONATAL CLIMBING FIBER-TO-PURKINJE CELL SYNAPSES

Development of cerebellar Purkinje cells (PCs) is modulated by neuroactive steroids. Developing hippocampal pyramidal neurons retrogradely release a pregnenolone sulfate (PregS)-like neurosteroid that may contribute to glutamatergic synapse stabilization. We hypothesized that PregS could exert a similar effect on developing PCs. To test this hypothesis, we performed whole-cell patch-clamp recordings from PCs in acute cerebellar vermis slices from neonatal rats. PregS induced a robust (similar to 3000%) and reversible increase in AMPA receptor-mediated miniature excitatory postsynaptic current (AMPA-mEPSC) frequency without affecting the amplitude, time-to-rise, or half-width of these events. PregS also increased the frequency of GABA(A) receptor-mediated miniature postsynaptic currents but to a significantly lesser extent (<100%). The PregS-induced increase of AMPA-mEPSC frequency was not significantly decreased by antagonists of receptors (NMDA, glycine, alpha 7 nicotinic acetylcholine and sigma 1) that have been shown to modulate glutamatergic transmission at PCs and/or mediate the actions of PregS on neurotransmitter release. Ca2+ chelation experiments suggested that PregS acts by increasing presynaptic terminal [Ca2+](i), an effect that is independent of voltage-gated Ca2+ channels, but is blocked by the antagonist of transient receptor potential (TRP) channels, La3+. PregS also increased the amplitude of EPSCs evoked by climbing fiber (CF) stimulation and decreased the paired-pulse ratio of these events. Neither CF nor parallel fiber-evoked EPSCs were affected by PregS in slices from juvenile rats. These results suggest that glutamate release at CF-to-PC synapses is an important target of PregS in the neonatal cerebellar cortex, an effect that may play a role in the refinement of these synapses. (C) 2011 IBRO. Published by Elsevier Ltd. All rights reserved.