Cell type-specific plasticity at parallel fiber synapses onto Purkinje cells in the posterior caudal lobe of the mormyrid fish cerebellum.

It has been demonstrated that there are two morphological subtypes of Purkinje cells (PCs)-fan-shaped Purkinje cells (fPCs) and multipolar Purkinje cells (mPCs)-in the posterior caudal lobe of the mormyrid fish cerebellum, but whether these cell types are also functionally distinct is unknown. Here, we have used electrophysiological and pharmacological tools in a slice preparation to demonstrate that pairing parallel fiber (PF) and climbing fiber (CF) inputs at a low frequency induces long-term depression (LTD) in fPCs but long-term potentiation (LTP) in mPCs. The induction of plasticity in both cell types required postsynaptic Ca2+ and type 1α metabotropic glutamate receptors. However, the LTD in fPCs was inducted via a calcium/calmodulin-dependent protein kinase II cascade, whereas LTP induction in mPCs required calcineurin. Moreover, the LTD in fPCs and LTP in mPCs were accompanied by changes to the corresponding paired-pulse ratios and their coefficients of variation, suggesting presynaptic modes of expression for the plasticity at PF terminals for both cell types. Hence, the synaptic plasticity at PF synapses onto PCs in the posterior caudal lobe of the mormyrid cerebellum is cell type specific, with both pre- and postsynaptic mechanisms contributing to its induction and expression. NEW & NOTEWORTHY Much has been learnt about the cerebellar long-term depression (LTD) in the cortex. More recent work has shown that long-term potentiation (LTP) is equally important for cerebellar motor learning. Here we report for the first time that plasticity in the mormyrid cerebellum is cell type specific, e.g., following the conventional pairing of parallel and climbing fiber inputs in an in vitro preparation leads to LTD in one Purkinje cell subtype and LTP in another.