A 3-synapse Positive Feedback Loop Regulates the Excitability of an Interneuron Critical for Sensitization in the Leech.
From: Department of Physiology and Biophysics, University of Miami School of Medicine, Miami, Florida 33136, USA. crisp@stolaf.edu
The Journal of neuroscience : the official journal of the Society for Neuroscience
- Publish Date: Mar 2006
- ISSN: 1529-2401
- Volume: 26
- Issue: 13
- Pages: 3524-31
- Medium: Internet
- Language: English
- Citation (JAMA): Crisp Kevin M, Muller Kenneth J, et al. A 3-synapse Positive Feedback Loop Regulates the Excitability of an Interneuron Critical for Sensitization in the Leech.. J. Neurosci. Mar 2006;26:3524-31
Abstract
Sensitization of reflexive shortening in the leech has been linked to serotonin (5-HT)-induced changes in the excitability of a single interneuron, the S cell. This neuron is necessary for sensitization and complete dishabituation of reflexive shortening, during which it contributes to the sensory-motor reflex. The S cell does not contain 5-HT, which is released primarily from the Retzius (R) cells, whose firing enhances S-cell excitability. Here, we show that the S cell excites the R cells, mainly via a fast disynaptic pathway in which the first synapse is the electrical junction between the S cell and the coupling interneurons, and the second synapse is a glutamatergic synapse of the coupling interneurons onto the R cells. The S cell-triggered excitatory postsynaptic potential in the R cell diminishes and nearly disappears in elevated concentrations of divalent cations because the coupling interneurons become inexcitable under these conditions. Serotonin released from the R cells feeds back on the S cell and increases its excitability by activating a 5-HT7-like receptor; 5-methoxytryptamine (5-MeOT; 10 microM) mimics the effects of 5-HT on S cell excitability, and effects of both 5-HT and 5-MeOT are blocked by pimozide (10 microM) and SB-269970 [(R)-3-(2-(2-(4-methylpiperidin-1-yl)-ethyl)pyrrolidine-1-sulfonyl)phenol] (5 microM). This feedback loop may be critical for the full expression of sensitization of reflexive shortening.
Mesh Headings (Keywords): Animals, Cells, Cultured, Differential Threshold, Excitatory Postsynaptic Potentials, Feedback, Interneurons, Leeches, Nerve Net, Neuronal Plasticity, Reflex, Synaptic Transmission
Check for Full Text / PubMed Unique Identifier (PMID): 16571760
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