Affiliation:
1. Université de Bordeaux, Centre National de la Recherche Scientifique (CNRS), Institut de Neurosciences Cognitives et Intégratives d'Aquitaine (INCIA), Biologie Animale, Talence Cedex, France
Abstract
Altering neuronal membrane properties, including input resistance, is a key modulatory mechanism for changing neural activity patterns. The effect of membrane currents generated by either synaptic or voltage-dependent channels directly depends on neuron input resistance. We found that local application of serotonin to different regions of identified motoneurons (MNs) of the postural/walking network of isolated crayfish produced different changes in input resistance. Puff-applied 5-HT in the periphery of the initial segment produced exclusively inhibitory responses. In contrast, when 5-HT was puff-applied on the central arbor of the same depressor (Dep) MN, exclusively depolarizing responses were obtained. Both inhibitory and excitatory responses were direct because they persisted in low-calcium saline. We found numerous close appositions between 5-HT-immunoreactive processes and the initial segment of dextran-rhodamine-filled Dep MNs. In contrast, almost no close apposition sites were found in Dep MN arbor. It seems that the 5-HT controls the level of excitability of postural network MNs by two mechanisms acting at two different sites: inhibitory responses (consistent with an action involving opening of K+ channels) occur in the initial segment region and may involve classic synaptic transmission, whereas depolarizing responses (consistent with an action involving closing of K+ channels) occur on MN branches via apparent paracrine effects.
Publisher
American Physiological Society
Subject
Physiology,General Neuroscience
Cited by
4 articles.
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