Certain patterns of neuronal activity lead to persistant decreases in synaptic strength, or long-term depressiion (LTD). LTD has been documented in many brain areas, including visual cortex, the hippocampus, and the cerebellum (Ito, 1989). In the cerebellar cortex, the Purkinje cells possess two separate sets of excitatory synapses, one from parallel fibers (granule cells axons) and one from climbing fibers (inferior olive axons). Both the parallel fibers and the climbing fiber synapses use glutamate as a neurotransmitter. Conjunctive stimulation (1-4Hz, for 25s to 10 min) of the parallel fibers and the climbing fibers produces a long-lasting depression of synaptic transmission at the synapses between the parallel fibers and Purkinje cells. The observed decrease in synaptic strength results from a reduction in the sensitivity of postsynaptic AMPA receptors (Ito et al 1982, and Crepel & Krupa 1988, Hirano 1991, Linden et al 1991).
Crepel, F. & Krupa, M. (1988) Activation of protein kinase C induces a long-term
depression of glutamate sensitivity of cerebellar Purkinje cells. An in vitro study. Brain
Hirano,T. (1991) Differential pre- and post-synaptic mechanisms for synaptic potentiation and depression between a granule cell and a Purkinje cell in rat cerebellar culture. Synapse 7:321-23
Ito, M. (1989) Long-term depression. Annu. Rev. Neurosci. 12:85-102
Ito, M., Sakurai, M., Tongroach, P. (1982) Climbing fiber induced depression of both mossy fiber responsiveness and glutamate sensitivity of cerebellar Purkinje cells. J. Physiol. 324:113-124
Linden, D.J. & Connor, J.A. (1991) Participation of postsynaptic PKC in cerebellar long-term depression in culture. Science. 254:1656-59
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