DEFINING A MINIMAL COMPUTATIONAL UNIT FOR CEREBELLAR LONG-TERM DEPRESSION

In cerebellar long-term depression (LTD), conjunctive stimulation of p arallel and climbing fiber inputs to a Purkinje neuron (PN) results in a selective depression of parallel fiber-PH synaptic strength. A simi lar phenomenon may be induced in the cultured PN when glutamate pulses and PH depolarization, which mimic the effects of parallel and climbi ng fibers, respectively, are coapplied. Here, we show that LTD can be induced in two very reduced preparations of the postsynaptic neuron; a n acutely dissociated preparation and a perforated outside-out macropa tch of dendritic membrane. LTD in these preparations retains propertie s of that seen in an intact cultured PH in that it is not induced by e ither glutamate pulses or depolarization alone and requires calcium in flux, mGluR activation, and PKC activation for induction. As both of t hese preparations lack dendritic spine compartments, these findings su ggest that the associative nature of LTD induction does not require th is level of morphological organization.