Journal
JOURNAL OF NEUROPHYSIOLOGY
Volume 109, Issue 11, Pages 2793-2802Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/jn.01063.2012
Keywords
Crustacea; stretch reflex; neuromodulation; posture; serotonin; cray-fish; 5-HT cell; paracrine
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Funding
- CNRS
- Agence Nationale de la Recherche (ANR) [NT05-1-41718]
- National Science Foundation [0135162, 0641326]
- Division Of Integrative Organismal Systems
- Direct For Biological Sciences [0641326, 1120291] Funding Source: National Science Foundation
- Division Of Integrative Organismal Systems
- Direct For Biological Sciences [0135162] Funding Source: National Science Foundation
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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.
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