Long-term surface stimulation of the cerebellum in the monkey. II. Electron microscopic and biochemical observations.

Phase and electron microscopy were used to study the effects of chronic intermittent or continuous stimulation applied to the surface of the cerebellum with bipolar platinum electrodes in monkeys. Damage under the anodes consisted of swelling of neuropil, variable loss of Purkinje cells, and a variable increase in fibrous glial processes. Under the cathode there was marked loss of Purkinje cells, thinning of the molecular layer, moderate swelling, occasional phagocytes with lipofuscin granules, and often an increase of fibrous glial processes. Despite the damage, normal appearing synaptic terminals remained in all layers under both anode and cathode, though sparser in fibrotic areas Gamma-aminobutyric acid (GABA) concentrations were decreased beneath the cathodes, reflecting the loss of Purkinje cells and other GABA-containing cells, and spermidine concentrations were increased in areas with increased fibrous glial processes.