title: Nonsynaptic plasticity underlies a compartmentalized increase in synaptic efficacy after classical conditioning.
abstract: It is now well documented in both vertebrates and invertebrates that nonsynaptic as well as synaptic plasticity can be a substrate for long-term memory [1-4]. Little is known, however, about how learning-induced nonsynaptic plasticity can lead to compartmentalized presynaptic changes underlying specific memory traces while leaving other circuit functions of the neuron unaffected. Here, using behavioral, electrophysiological, and optical recording methods, we show that the previously described learning-induced depolarization of a modulatory neuron [5] of the Lymnaea feeding system affects its axonal terminals in a spatially segregated manner. In a side branch of the axon of the cerebral giant cells (CGCs), classical conditioning of intact animals reduced proximal-to-distal attenuation of spike-evoked calcium transients, providing a highly effective mechanism for a compartmentalized increase in synaptic efficacy. Somatic depolarization by current injection, which spreads onto the CGC's axonal side branch [5], and the blocking of A-type potassium channels with 4-aminopyridine had an effect similar to learning on the calcium transients. Both of these experimental manipulations also reduced axonal spike attenuation. These findings suggest that the voltage-dependent inactivation of an A-type potassium current links global nonsynaptic changes to compartmentalized synaptic changes.
authors.affiliation: Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences, Moscow 117485, Russian Federation.
authors.forename: Evgeny S
authors.initials: ES
authors.lastname: Nikitin
authors.forename: Pavel M
authors.initials: PM
authors.lastname: Balaban
authors.forename: György
authors.initials: G
authors.lastname: Kemenes
mesh_terms: D000704:Analysis of Variance; D000814:Aniline Compounds; D000818:Animals; D001369:Axons / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D003214:Conditioning, Classical / Q000502:physiology*; D005452:Fluoresceins; D015726:Giant Cells / Q000378:metabolism; D008195:Lymnaea / Q000502:physiology*; D057567:Memory, Long-Term / Q000502:physiology*; D018613:Microscopy, Confocal; D009473:Neuronal Plasticity / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D013569:Synapses / Q000502:physiology*
chemical_list: D000814:Aniline Compounds; D005452:Fluoresceins; C503942:Oregon green 488 BAPTA-1; D011188:Potassium; D002118:Calcium