Permissive role of interneurons in corticostriatal synaptic plasticity

Two different forms of synaptic plasticity have been found at corticostriat al synapses: long-term depression (LTD) and long-term potentiation (LTP). B oth these enduring changes in the efficacy of excitatory neurotransmission in the striatum have a major impact on the physiological activity of the ba sal ganglia and are triggered by the stimulation of complex and independent cascades of intracellular second messenger systems. Striatal LTD and LTP a re evoked following the repetitive stimulation of corticostriatal fibers an d are dependent on the glutamate ionotropic receptor subtype activated. Rec ent experimental evidence indicates that two different subtypes of interneu rons attend in the correct processing of information flow arising from the cortex and leading to striatal LTD or LTP. Acetylcholine (Ach) and nitric o xide (NO) producing striatal interneurons, in fact, are activated by the co rtex during the induction phase of striatal plasticity, and stimulate, in t urn, the intracellular changes in projection neurons required for LTD or LT P. Interneurons, therefore, exerts a feed-forward control of the excitabili ty of striatal projection neurons ensuring the coordinate expression of two alternative forms of synaptic plasticity at the same type of excitatory sy napse. (C) 1999 Elsevier Science B.V. All rights reserved.