INCREASE IN THE EFFICACY OF SYNAPSES BETWEEN PARALLEL FIBERS AND PURKINJE CELLS AFTER JOINT STIMULATION OF CLIMBING AND PARALLEL FIBERS IN THE FROG

A study was made of the susceptibility of Purkinje cells to long-term plasticity changes produced by joint stimulation of two inputs: the parallel and the climbing fibers. Experiments were conducted on a preparation of isolated frog cerebellum, joined to the medulla by one peduncle. A total of 18 neurons were investigated which showed a monosynaptic response to stimulation of the parallel fibers and maintained stable background activity over a 2 h period. Curves were plotted throughout this time for the likelihood of a reaction occurring in Purkinje cells in response to stimulation of the parallel fibers. Level of current required to stimulate a Purkinje cell firing index of 0.5 (I0.5) was calculated. Neurons in which compound response to the "climber" type had been produced by stimulating the medulla showed a I0.5 of 0.7 (less than one unit) at the start and finish of experiments, which would suggest an increase in the efficacy of the synapses of parallel fibers in Purkinje cells when parallel and climbing fibers are stimulated simultaneously.